© 2015 Pearson Education, Inc.

Introduction The plasma membrane and its proteins enable cells to
survive and function. Aquaporins are membrane proteins that function as water channels. © 2015 Pearson Education, Inc. 2

Introduction This chapter addresses how working cells use membranes,
energy, and enzymes. © 2015 Pearson Education, Inc. 3

Membrane Structure and Function
© 2015 Pearson Education, Inc. 4

Membranes are fluid mosaics of lipids and proteins with many functions
Biologists use the fluid mosaic model to describe a membrane’s structure, a patchwork of diverse protein molecules embedded in a phospholipid bilayer. The plasma membrane exhibits selective permeability. The proteins embedded in a membrane’s phospholipid bilayer perform various functions. Teaching Tips You might wish to share a very simple analogy that seems to work well for some students. A cell membrane is a little like a peanut butter and jelly sandwich with jelly beans poked into it. The bread represents the hydrophilic portions of the bilayer (and bread does indeed quickly absorb water). The peanut butter and jelly represent the hydrophobic regions (and peanut butter, containing plenty of oil, is generally hydrophobic). The jelly beans stuck into the sandwich represent proteins variously embedded partially into or completely through the membrane. Transport proteins would be like the jelly beans that poke completely through the sandwich. Analogies are rarely perfect. Challenge your students to critique this analogy by finding exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.) © 2015 Pearson Education, Inc. 5

Cytoplasmic side of membrane Extracellular side of membrane
Figure 5.1 Cytoplasmic side of membrane Extracellular side of membrane O2 CO2 Fibers of extracellular matrices (ECM) Phospholipid Cholesterol Membrane proteins Figure 5.1 Diverse functions of the plasma membrane Microfilaments of cytoskeleton

Diffusion of small nonpolar molecules
Figure 5.1-2 CO2 O2 Diffusion of small nonpolar molecules Figure Diverse functions of the plasma membrane (part 2)

Active transport protein Channel protein
Figure 5.1-3 Solute molecules Active transport protein Channel protein Figure Diverse functions of the plasma membrane (part 3) ATP Transport Proteins Allow specific ions or molecules to enter or exit the cell

Some membrane proteins are enzymes
Figure 5.1-4 Initial reactant Enzymes Product of reaction Enzymes Figure Diverse functions of the plasma membrane (part 4) Some membrane proteins are enzymes Enzymes may be grouped to carry out sequential reactions

Microfilaments of cytoskeleton
Figure 5.1-5 Extracellular matrix Attachment protein Microfilaments of cytoskeleton Figure Diverse functions of the plasma membrane (part 5) Attachment Proteins Attach to the extracellular matrix and cytoskeleton Help support the membrane Can coordinate external and internal changes

Signaling molecules bind to receptor proteins
Figure 5.1-6 Signaling molecule Receptor protein Figure Diverse functions of the plasma membrane (part 6) Receptor Proteins Signaling molecules bind to receptor proteins Receptor proteins relay the message by activating other molecules inside the cell

Form intercellular junctions that attach adjacent cells
Figure 5.1-7 Junction protein Junction protein Figure Diverse functions of the plasma membrane (part 7) Junction Proteins Form intercellular junctions that attach adjacent cells

Protein that recognizes neighboring cell
Figure 5.1-8 Protein that recognizes neighboring cell Attached sugars Glycoprotein Figure Diverse functions of the plasma membrane (part 8) Glycoproteins Serve as ID tags May be recognized by membrane proteins of other cells

Cytoplasmic side of membrane Extracellular side of membrane
Figure 5.1-9 Cytoplasmic side of membrane Extracellular side of membrane O2 CO2 Diffusion of small nonpolar molecules Fibers of extracellular matrices (ECM) Enzyme Enzyme Phospholipid Cholesterol Receptor protein Attachment protein Figure Diverse functions of the plasma membrane (part 9) Junction protein Channel protein Junction protein Active transport protein ATP Glyco- protein Microfilaments of cytoskeleton

The spontaneous formation of membranes was a critical step in the origin of life
Phospholipids, the key ingredient of biological membranes, spontaneously self-assemble into simple membranes. The formation of membrane-enclosed collections of molecules was a critical step in the evolution of the first cells. Teaching Tips The hydrophobic and hydrophilic ends of a phospholipid molecule create a lipid bilayer. The hydrophobic edges of the layer will also seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water. Furthermore, because of these hydrophobic properties, lipid bilayers are naturally self-healing. All of these properties emerge from the structure of phospholipids. © 2015 Pearson Education, Inc. 15

Water-filled bubble made of phospholipids
Figure 5.2 Water-filled bubble made of phospholipids Figure 5.2 Artificial membrane-bounded sacs

Passive transport is diffusion across a membrane with no energy investment
Diffusion is the tendency of particles to spread out evenly in an available space. Particles move from an area of more concentrated particles to an area where they are less concentrated. This means that particles diffuse down their concentration gradient. Eventually, the particles reach dynamic equilibrium, where there is no net change in concentration on either side of the membrane. Student Misconceptions and Concerns For students with limited science backgrounds, concepts such as diffusion and osmosis can take considerable time to fully understand and apply. Instructors often struggle to remember a time in our lives when we did not know about such fundamental scientific principles. Consider spending extra time to illustrate and demonstrate these key processes to the class. Consider short interactive class exercises in which students create analogies or think of examples of these principles in their lives. Teaching Tips Students often benefit from reminders of diffusion in their lives. Smells can usually be traced back to their sources—the smell of dinner on the stove, the scent of perfume or cologne from a bottle, the smoke drifting away from a campfire. These scents are strongest nearest the source and weaker as we move away. Active Lecture Tips Consider demonstrating simple diffusion. A large jar of water and a few drops of dark-colored dye work well over the course of a lecture period. Alternatively, release a strong scent of cologne or peppermint or peel part of an orange in the classroom and have students raise their hands as they first detect the smell. Students nearest the source will raise their hands before students farther away. A fan from a projector or overhead vent may bias the experiment a bit, so be aware of any directed movements of air in your classroom that might disrupt this demonstration. © 2015 Pearson Education, Inc. 17

Molecules of dye Membrane Pores Net diffusion Net diffusion
Figure 5.3a Molecules of dye Membrane Pores Net diffusion Figure 5.3a Diffusion of one type of molecule across a membrane Net diffusion Equilibrium

Net diffusion Net diffusion Equilibrium Net diffusion Net diffusion
Figure 5.3b Net diffusion Net diffusion Equilibrium Figure 5.3b Diffusion of two types of molecules across a membrane Net diffusion Net diffusion Equilibrium

Passive transport is diffusion across a membrane with no energy investment
Diffusion across a cell membrane does not require energy, so it is called passive transport. Diffusion down concentration gradients is the sole means by which oxygen enters your cells and carbon dioxide passes out of cells. Student Misconceptions and Concerns For students with limited science backgrounds, concepts such as diffusion and osmosis can take considerable time to fully understand and apply. Instructors often struggle to remember a time in our lives when we did not know about such fundamental scientific principles. Consider spending extra time to illustrate and demonstrate these key processes to the class. Consider short interactive class exercises in which students create analogies or think of examples of these principles in their lives. Teaching Tips Students often benefit from reminders of diffusion in their lives. Smells can usually be traced back to their sources—the smell of dinner on the stove, the scent of perfume or cologne from a bottle, the smoke drifting away from a campfire. These scents are strongest nearest the source and weaker as we move away. Active Lecture Tips Consider demonstrating simple diffusion. A large jar of water and a few drops of dark-colored dye work well over the course of a lecture period. Alternatively, release a strong scent of cologne or peppermint or peel part of an orange in the classroom and have students raise their hands as they first detect the smell. Students nearest the source will raise their hands before students farther away. A fan from a projector or overhead vent may bias the experiment a bit, so be aware of any directed movements of air in your classroom that might disrupt this demonstration. © 2015 Pearson Education, Inc. 20

Osmosis is the diffusion of water across a membrane
One of the most important substances that crosses membranes by passive transport is water. The diffusion of water across a selectively permeable membrane is called osmosis. Student Misconceptions and Concerns For students with limited science backgrounds, concepts such as diffusion and osmosis can take considerable time to fully understand and apply. Instructors often struggle to remember a time in our lives when we did not know about such fundamental scientific principles. Consider spending extra time to illustrate and demonstrate these key processes to the class. Consider short interactive class exercises in which students create analogies or think of examples of these principles in their lives. Teaching Tips Your students may have noticed that the skin of their fingers wrinkles after taking a long shower or bath, or after washing dishes. The skin wrinkles because it is swollen with water but still tacked down at some points. Through osmosis, water moves into the epidermal skin cells. Our skin is hypertonic to these solutions, producing the swelling that appears as large wrinkles. Oils inhibit the movement of water into our skin. Thus, soapy water results in wrinkling faster than plain water because the soap removes the natural layer of oil from our skin. Active Lecture Tips See the Activity Using Food and Drink to Describe Osmosis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc. 21

Osmosis is the diffusion of water across a membrane
If a membrane, permeable to water but not to a solute, separates two solutions with different concentrations of solute, water will cross the membrane, moving down its own concentration gradient, until the solute concentration on both sides is equal. Student Misconceptions and Concerns For students with limited science backgrounds, concepts such as diffusion and osmosis can take considerable time to fully understand and apply. Instructors often struggle to remember a time in our lives when we did not know about such fundamental scientific principles. Consider spending extra time to illustrate and demonstrate these key processes to the class. Consider short interactive class exercises in which students create analogies or think of examples of these principles in their lives. Teaching Tips Your students may have noticed that the skin of their fingers wrinkles after taking a long shower or bath, or after washing dishes. The skin wrinkles because it is swollen with water but still tacked down at some points. Through osmosis, water moves into the epidermal skin cells. Our skin is hypertonic to these solutions, producing the swelling that appears as large wrinkles. Oils inhibit the movement of water into our skin. Thus, soapy water results in wrinkling faster than plain water because the soap removes the natural layer of oil from our skin. Active Lecture Tips See the Activity Using Food and Drink to Describe Osmosis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc. 22

Lower concentration of solute Higher concentration of solute
Figure 5.4 Lower concentration of solute Higher concentration of solute More equal concentrations of solute H2O Solute molecule Selectively permeable membrane Water molecule Figure 5.4 Osmosis, the diffusion of water across a membrane Solute molecule with cluster of water molecules Osmosis

Water balance between cells and their surroundings is crucial to organisms
Tonicity is a term that describes the ability of a surrounding solution to cause a cell to gain or lose water. The tonicity of a solution mainly depends on its concentration of solutes relative to the concentration of solutes inside the cell. Student Misconceptions and Concerns Students easily confuse the term hypertonic and hypotonic. One challenge is to get students to understand that these are relative terms, such as heavier, darker, or fewer. No single object is heavier, no single cup of coffee is darker, and no single bag of M&M’s has fewer candies. Such terms only apply when comparing two or more items. A solution with a higher concentration than another solution is hypertonic to that solution. However, the same solution might also be hypotonic to a third solution. Teaching Tips The word root “hypo” means below. Thus, a hypodermic needle injects substances below the dermis. Students might best remember that hypotonic solutions have concentrations of solutes below that of the other solution(s). After introducing the idea of hypertonic and hypotonic solutions, you may wish to challenge your students with the following: A salmon might swim from the ocean up a freshwater stream to reproduce. The salmon is moving from a _____ environment to a _____ environment. (Answers: hypertonic, hypotonic) The effects of hypertonic and hypotonic solutions can be demonstrated if students soak carrot sticks, long slices of potato, or celery in hypertonic and hypotonic solutions. These also make nice class demonstrations. © 2015 Pearson Education, Inc. 24

How will animal cells be affected when placed into solutions of various tonicities? In an isotonic solution, the concentration of solute is the same on both sides of a membrane, and the cell volume will not change. In a hypotonic solution, the solute concentration is lower outside the cell, water molecules move into the cell, and the cell will expand and may burst. In a hypertonic solution, the solute concentration is higher outside the cell, water molecules move out of the cell, and the cell will shrink. Student Misconceptions and Concerns Students easily confuse the term hypertonic and hypotonic. One challenge is to get students to understand that these are relative terms, such as heavier, darker, or fewer. No single object is heavier, no single cup of coffee is darker, and no single bag of M&M’s has fewer candies. Such terms only apply when comparing two or more items. A solution with a higher concentration than another solution is hypertonic to that solution. However, the same solution might also be hypotonic to a third solution. Teaching Tips The word root “hypo” means below. Thus, a hypodermic needle injects substances below the dermis. Students might best remember that hypotonic solutions have concentrations of solutes below that of the other solution(s). After introducing the idea of hypertonic and hypotonic solutions, you may wish to challenge your students with the following: A salmon might swim from the ocean up a freshwater stream to reproduce. The salmon is moving from a _____ environment to a _____ environment. (Answers: hypertonic, hypotonic) The effects of hypertonic and hypotonic solutions can be demonstrated if students soak carrot sticks, long slices of potato, or celery in hypertonic and hypotonic solutions. These also make nice class demonstrations. © 2015 Pearson Education, Inc. 25

Hypotonic solution (lower solute levels)
Figure 5.5 Hypotonic solution (lower solute levels) Isotonic solution (equal solute levels) Hypertonic solution (higher solute levels) H2O H2O H2O H2O Animal cell Lysed Normal Shriveled Figure 5.5 How animal and plant cells react to changes in tonicity

For an animal cell to survive in a hypotonic or hypertonic environment, it must engage in osmoregulation, the control of water balance. Student Misconceptions and Concerns Students easily confuse the term hypertonic and hypotonic. One challenge is to get students to understand that these are relative terms, such as heavier, darker, or fewer. No single object is heavier, no single cup of coffee is darker, and no single bag of M&M’s has fewer candies. Such terms only apply when comparing two or more items. A solution with a higher concentration than another solution is hypertonic to that solution. However, the same solution might also be hypotonic to a third solution. Teaching Tips The word root “hypo” means below. Thus, a hypodermic needle injects substances below the dermis. Students might best remember that hypotonic solutions have concentrations of solutes below that of the other solution(s). After introducing the idea of hypertonic and hypotonic solutions, you may wish to challenge your students with the following: A salmon might swim from the ocean up a freshwater stream to reproduce. The salmon is moving from a _____ environment to a _____ environment. (Answers: hypertonic, hypotonic) The effects of hypertonic and hypotonic solutions can be demonstrated if students soak carrot sticks, long slices of potato, or celery in hypertonic and hypotonic solutions. These also make nice class demonstrations. © 2015 Pearson Education, Inc. 27

The cell walls of plant cells, prokaryotes, and fungi make water balance issues somewhat different.
The cell wall of a plant cell exerts pressure that prevents the cell from taking in too much water and bursting when placed in a hypotonic environment. But in a hypertonic environment, plant and animal cells both shrivel. Student Misconceptions and Concerns Students easily confuse the term hypertonic and hypotonic. One challenge is to get students to understand that these are relative terms, such as heavier, darker, or fewer. No single object is heavier, no single cup of coffee is darker, and no single bag of M&M’s has fewer candies. Such terms only apply when comparing two or more items. A solution with a higher concentration than another solution is hypertonic to that solution. However, the same solution might also be hypotonic to a third solution. Teaching Tips The word root “hypo” means below. Thus, a hypodermic needle injects substances below the dermis. Students might best remember that hypotonic solutions have concentrations of solutes below that of the other solution(s). After introducing the idea of hypertonic and hypotonic solutions, you may wish to challenge your students with the following: A salmon might swim from the ocean up a freshwater stream to reproduce. The salmon is moving from a _____ environment to a _____ environment. (Answers: hypertonic, hypotonic) The effects of hypertonic and hypotonic solutions can be demonstrated if students soak carrot sticks, long slices of potato, or celery in hypertonic and hypotonic solutions. These also make nice class demonstrations. © 2015 Pearson Education, Inc. 28

Hypotonic solution (lower solute levels)
Figure 5.5 Hypotonic solution (lower solute levels) Isotonic solution (equal solute levels) Hypertonic solution (higher solute levels) Plasma membrane H2O H2O H2O Plant cell Turgid (normal) Flaccid Shriveled (plasmolyzed) Figure 5.5 How animal and plant cells react to changes in tonicity

Transport proteins can facilitate diffusion across membranes
Hydrophobic substances easily diffuse across a cell membrane. However, polar or charged substances do not easily cross cell membranes and, instead, move across membranes with the help of specific transport proteins in a process called facilitated diffusion, which does not require energy and relies on the concentration gradient. Teaching Tips The text notes that “The greater the number of transport proteins for a particular solute in a membrane, the faster the solute’s rate of diffusion across the membrane.” This is similar to a situation that might be more familiar to your students. The more ticket-takers present at the entrance to a stadium, the faster the rate of movement of people into the stadium. © 2015 Pearson Education, Inc. 30 30

Solute molecule Transport protein Figure 5.6
Figure 5.6 Transport protein providing a channel for the diffusion of a specific solute across a membrane

Some proteins function by becoming a hydrophilic tunnel for passage of ions or other molecules.
Other proteins bind their passenger, change shape, and release their passenger on the other side. In both cases, the transport protein helps a specific substance diffuse across the membrane down its concentration gradient and thus requires no input of energy. Teaching Tips The text notes that “The greater the number of transport proteins for a particular solute in a membrane, the faster the solute’s rate of diffusion across the membrane.” This is similar to a situation that might be more familiar to your students. The more ticket-takers present at the entrance to a stadium, the faster the rate of movement of people into the stadium. © 2015 Pearson Education, Inc. 32 32

Because water is polar, its diffusion through a membrane’s hydrophobic interior is relatively slow.
The very rapid diffusion of water into and out of certain cells is made possible by a protein channel called an aquaporin. Teaching Tips The text notes that “The greater the number of transport proteins for a particular solute in a membrane, the faster the solute’s rate of diffusion across the membrane.” This is similar to a situation that might be more familiar to your students. The more ticket-takers present at the entrance to a stadium, the faster the rate of movement of people into the stadium. © 2015 Pearson Education, Inc. 33 33

Cells expend energy in the active transport of a solute
In active transport, a cell must expend energy to move a solute against its concentration gradient. The energy molecule ATP supplies the energy for most active transport. The following figures show the four main stages of active transport. Teaching Tips • Active transport uses energy to move a solute against its concentration gradient. Challenge your students to think of the many possible analogies to this situation, for example, bailing out a leaky boat by moving water back to a place (outside the boat) where water is more concentrated. An alternative analogy might be the herding of animals, which requires work to keep the organisms concentrated and counteract their natural tendency to spread out. • Students familiar with city subway toll stations might think of some gate mechanisms that work similarly to the proteins regulating active transport. A person steps up to a barrier and inserts payment (analogous to ATP input), and the gate changes shape, permitting passage to the other side. Even a simple turnstile system that requires payment is generally similar. © 2015 Pearson Education, Inc. 34

Solute binds to transport protein.
Figure 5.8-1 Transport protein Solute 1 Solute binds to transport protein. Figure Active transport of a solute across a membrane (step 1)

Figure 5.8-2 Transport protein ATP Solute 1 Solute binds to transport protein. 2 ATP provides energy for change in protein shape. Figure Active transport of a solute across a membrane (step 2)

Figure 5.8-3 Transport protein ATP Solute 1 Solute binds to transport protein. 2 ATP provides energy for change in protein shape. 3 Protein returns to original shape and more solute can bind. Figure Active transport of a solute across a membrane (step 3)

Exocytosis and endocytosis transport large molecules across membranes
A cell uses two mechanisms to move large molecules across membranes. Exocytosis is used to export bulky molecules, such as proteins or polysaccharides. Endocytosis is used to take in large molecules. In both cases, material to be transported is packaged within a vesicle that fuses with the membrane. Active Lecture Tips Students carefully considering exocytosis may notice that membrane from secretory vesicles is added to the plasma membrane. Challenge your students to work with someone sitting nearby to identify mechanisms that balance out this enlargement of the cell surface. (Endocytosis “subtracts” area from the cell surface. It is a major factor balancing out the additional membrane supplied by exocytosis.) © 2015 Pearson Education, Inc. 38

There are two kinds of endocytosis.
Phagocytosis is the engulfment of a particle by the cell wrapping cell membrane around it, forming a vacuole. Receptor-mediated endocytosis uses membrane receptors for specific solutes. The region of the membrane with receptors pinches inward to form a vesicle. Receptor-mediated endocytosis is used to take in cholesterol from the blood. Active Lecture Tips Students carefully considering exocytosis may notice that membrane from secretory vesicles is added to the plasma membrane. Challenge your students to work with someone sitting nearby to identify mechanisms that balance out this enlargement of the cell surface. (Endocytosis “subtracts” area from the cell surface. It is a major factor balancing out the additional membrane supplied by exocytosis.) © 2015 Pearson Education, Inc. 39

“Food” or other particle
Figure 5.9-0 Phagocytosis EXTRACELLULAR FLUID CYTOPLASM Pseudopodium “Food” or other particle Food vacuole Receptor-mediated endocytosis Coat protein Coated vesicle Receptor Figure Two kinds of endocytosis Coated pit Specific molecule

“Food” or other particle
Figure 5.9-1 Phagocytosis EXTRACELLULAR FLUID CYTOPLASM Pseudopodium “Food” or other particle Food vacuole Figure Two kinds of endocytosis (part 1)

Receptor-mediated endocytosis Coat protein
Figure 5.9-2 Receptor-mediated endocytosis Coat protein Coated vesicle Receptor Coated pit Specific molecule Figure Two kinds of endocytosis (part 2)

Energy and the Cell 43

Cells transform energy as they perform work
Cells are miniature chemical factories, housing thousands of chemical reactions. Some of these chemical reactions release energy, and others require energy. Student Misconceptions and Concerns Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy. They also may not have distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. Teaching Tips • Some students can relate well to the concept of entropy as applied to the room where they live. Despite cleaning up and organizing the room on a regular (or irregular) basis, the room becomes increasingly disorganized, a victim of entropy, until another energy input (or effort) is exerted to make the room more orderly again. Students might even get to know entropy as the “dorm room effect.” • The heat produced by the engine of a car is typically used to heat the car during cold weather. However, is this same heat available in warmer weather? Students are often unaware that their car “heaters” work very well in the summer, too. Just as exercise can warm us when it is cold, the same extra heat is released when we exercise in warm conditions. A car engine in the summer struggles to dissipate heat in the same way that a human struggles to cool off after exercising when the weather is warm. Active Lecture Tips • Challenge your students to come up with examples of common energy conversions in their lives. Have students turn to someone seated near them to find at least two examples. In our daily lives, we rely upon many energy transformations. On our classroom walls, a clock converts electrical energy to mechanical energy to sweep the hands around the clock’s face (unless it is digital!). Our physical (mechanical) activities walking to and from the classroom rely upon the chemical energy from our diet. This chemical energy in our diet also helps us maintain a steady body temperature (heat). • Challenge your students to explain why they feel warm when it is 30C (86F) outside if their core body temperature is 37C (98.6F). Shouldn’t they feel cold? Have students work in groups of two or three to think this through. The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a core body temperature around 37C. Thus, we sweat and behave in ways that help release our extra heat generated in cellular respiration. • See the Activity Keeping an Organized Dorm Room Requires Energy, Just Like in a Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. • See the Activity Universal Currency in the Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 44

Energy is the capacity to cause change or to perform work.
There are two basic forms of energy. Kinetic energy is the energy of motion. Potential energy is energy that matter possesses as a result of its location or structure. Student Misconceptions and Concerns Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy. They also may not have distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. Teaching Tips • Some students can relate well to the concept of entropy as applied to the room where they live. Despite cleaning up and organizing the room on a regular (or irregular) basis, the room becomes increasingly disorganized, a victim of entropy, until another energy input (or effort) is exerted to make the room more orderly again. Students might even get to know entropy as the “dorm room effect.” • The heat produced by the engine of a car is typically used to heat the car during cold weather. However, is this same heat available in warmer weather? Students are often unaware that their car “heaters” work very well in the summer, too. Just as exercise can warm us when it is cold, the same extra heat is released when we exercise in warm conditions. A car engine in the summer struggles to dissipate heat in the same way that a human struggles to cool off after exercising when the weather is warm. Active Lecture Tips • Challenge your students to come up with examples of common energy conversions in their lives. Have students turn to someone seated near them to find at least two examples. In our daily lives, we rely upon many energy transformations. On our classroom walls, a clock converts electrical energy to mechanical energy to sweep the hands around the clock’s face (unless it is digital!). Our physical (mechanical) activities walking to and from the classroom rely upon the chemical energy from our diet. This chemical energy in our diet also helps us maintain a steady body temperature (heat). • Challenge your students to explain why they feel warm when it is 30C (86F) outside if their core body temperature is 37C (98.6F). Shouldn’t they feel cold? Have students work in groups of two or three to think this through. The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a core body temperature around 37C. Thus, we sweat and behave in ways that help release our extra heat generated in cellular respiration. • See the Activity Keeping an Organized Dorm Room Requires Energy, Just Like in a Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. • See the Activity Universal Currency in the Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 45

Thermal energy in transfer from one object to another is called heat.
Thermal energy is a type of kinetic energy associated with the random movement of atoms or molecules. Thermal energy in transfer from one object to another is called heat. Light is also a type of kinetic energy; it can be harnessed to power photosynthesis. Student Misconceptions and Concerns Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy. They also may not have distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. Teaching Tips • Some students can relate well to the concept of entropy as applied to the room where they live. Despite cleaning up and organizing the room on a regular (or irregular) basis, the room becomes increasingly disorganized, a victim of entropy, until another energy input (or effort) is exerted to make the room more orderly again. Students might even get to know entropy as the “dorm room effect.” • The heat produced by the engine of a car is typically used to heat the car during cold weather. However, is this same heat available in warmer weather? Students are often unaware that their car “heaters” work very well in the summer, too. Just as exercise can warm us when it is cold, the same extra heat is released when we exercise in warm conditions. A car engine in the summer struggles to dissipate heat in the same way that a human struggles to cool off after exercising when the weather is warm. Active Lecture Tips • Challenge your students to come up with examples of common energy conversions in their lives. Have students turn to someone seated near them to find at least two examples. In our daily lives, we rely upon many energy transformations. On our classroom walls, a clock converts electrical energy to mechanical energy to sweep the hands around the clock’s face (unless it is digital!). Our physical (mechanical) activities walking to and from the classroom rely upon the chemical energy from our diet. This chemical energy in our diet also helps us maintain a steady body temperature (heat). • Challenge your students to explain why they feel warm when it is 30C (86F) outside if their core body temperature is 37C (98.6F). Shouldn’t they feel cold? Have students work in groups of two or three to think this through. The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a core body temperature around 37C. Thus, we sweat and behave in ways that help release our extra heat generated in cellular respiration. • See the Activity Keeping an Organized Dorm Room Requires Energy, Just Like in a Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. • See the Activity Universal Currency in the Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 46

Chemical energy is the potential energy available for release in a chemical reaction and the most important type of energy for living organisms to power the work of the cell. Student Misconceptions and Concerns Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy. They also may not have distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. Teaching Tips • Some students can relate well to the concept of entropy as applied to the room where they live. Despite cleaning up and organizing the room on a regular (or irregular) basis, the room becomes increasingly disorganized, a victim of entropy, until another energy input (or effort) is exerted to make the room more orderly again. Students might even get to know entropy as the “dorm room effect.” • The heat produced by the engine of a car is typically used to heat the car during cold weather. However, is this same heat available in warmer weather? Students are often unaware that their car “heaters” work very well in the summer, too. Just as exercise can warm us when it is cold, the same extra heat is released when we exercise in warm conditions. A car engine in the summer struggles to dissipate heat in the same way that a human struggles to cool off after exercising when the weather is warm. Active Lecture Tips • Challenge your students to come up with examples of common energy conversions in their lives. Have students turn to someone seated near them to find at least two examples. In our daily lives, we rely upon many energy transformations. On our classroom walls, a clock converts electrical energy to mechanical energy to sweep the hands around the clock’s face (unless it is digital!). Our physical (mechanical) activities walking to and from the classroom rely upon the chemical energy from our diet. This chemical energy in our diet also helps us maintain a steady body temperature (heat). • Challenge your students to explain why they feel warm when it is 30C (86F) outside if their core body temperature is 37C (98.6F). Shouldn’t they feel cold? Have students work in groups of two or three to think this through. The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a core body temperature around 37C. Thus, we sweat and behave in ways that help release our extra heat generated in cellular respiration. • See the Activity Keeping an Organized Dorm Room Requires Energy, Just Like in a Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. • See the Activity Universal Currency in the Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 47

Thermodynamics is the study of energy transformations that occur in a collection of matter.
The word system is used for the matter under study. The word surroundings is used for everything outside the system; the rest of the universe. Student Misconceptions and Concerns Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy. They also may not have distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. Teaching Tips • Some students can relate well to the concept of entropy as applied to the room where they live. Despite cleaning up and organizing the room on a regular (or irregular) basis, the room becomes increasingly disorganized, a victim of entropy, until another energy input (or effort) is exerted to make the room more orderly again. Students might even get to know entropy as the “dorm room effect.” • The heat produced by the engine of a car is typically used to heat the car during cold weather. However, is this same heat available in warmer weather? Students are often unaware that their car “heaters” work very well in the summer, too. Just as exercise can warm us when it is cold, the same extra heat is released when we exercise in warm conditions. A car engine in the summer struggles to dissipate heat in the same way that a human struggles to cool off after exercising when the weather is warm. Active Lecture Tips • Challenge your students to come up with examples of common energy conversions in their lives. Have students turn to someone seated near them to find at least two examples. In our daily lives, we rely upon many energy transformations. On our classroom walls, a clock converts electrical energy to mechanical energy to sweep the hands around the clock’s face (unless it is digital!). Our physical (mechanical) activities walking to and from the classroom rely upon the chemical energy from our diet. This chemical energy in our diet also helps us maintain a steady body temperature (heat). • Challenge your students to explain why they feel warm when it is 30C (86F) outside if their core body temperature is 37C (98.6F). Shouldn’t they feel cold? Have students work in groups of two or three to think this through. The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a core body temperature around 37C. Thus, we sweat and behave in ways that help release our extra heat generated in cellular respiration. • See the Activity Keeping an Organized Dorm Room Requires Energy, Just Like in a Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. • See the Activity Universal Currency in the Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 48

Two laws govern energy transformations in organisms.
Per the first law of thermodynamics (also known as the law of energy conservation), energy in the universe is constant. Per the second law of thermodynamics, energy conversions increase the disorder of the universe. Entropy is the measure of disorder or randomness. Student Misconceptions and Concerns Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy. They also may not have distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. Teaching Tips • Some students can relate well to the concept of entropy as applied to the room where they live. Despite cleaning up and organizing the room on a regular (or irregular) basis, the room becomes increasingly disorganized, a victim of entropy, until another energy input (or effort) is exerted to make the room more orderly again. Students might even get to know entropy as the “dorm room effect.” • The heat produced by the engine of a car is typically used to heat the car during cold weather. However, is this same heat available in warmer weather? Students are often unaware that their car “heaters” work very well in the summer, too. Just as exercise can warm us when it is cold, the same extra heat is released when we exercise in warm conditions. A car engine in the summer struggles to dissipate heat in the same way that a human struggles to cool off after exercising when the weather is warm. Active Lecture Tips • Challenge your students to come up with examples of common energy conversions in their lives. Have students turn to someone seated near them to find at least two examples. In our daily lives, we rely upon many energy transformations. On our classroom walls, a clock converts electrical energy to mechanical energy to sweep the hands around the clock’s face (unless it is digital!). Our physical (mechanical) activities walking to and from the classroom rely upon the chemical energy from our diet. This chemical energy in our diet also helps us maintain a steady body temperature (heat). • Challenge your students to explain why they feel warm when it is 30C (86F) outside if their core body temperature is 37C (98.6F). Shouldn’t they feel cold? Have students work in groups of two or three to think this through. The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a core body temperature around 37C. Thus, we sweat and behave in ways that help release our extra heat generated in cellular respiration. • See the Activity Keeping an Organized Dorm Room Requires Energy, Just Like in a Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. • See the Activity Universal Currency in the Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 49

In the car and cells, the waste products are carbon dioxide and water.
Automobile engines and cells use the same basic process to make the chemical energy of their fuel available for work. In the car and cells, the waste products are carbon dioxide and water. Cells use oxygen in reactions that release energy from fuel molecules. In cellular respiration, the chemical energy stored in organic molecules is used to produce ATP, which the cell can use to perform work. Student Misconceptions and Concerns Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy. They also may not have distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. Teaching Tips • Some students can relate well to the concept of entropy as applied to the room where they live. Despite cleaning up and organizing the room on a regular (or irregular) basis, the room becomes increasingly disorganized, a victim of entropy, until another energy input (or effort) is exerted to make the room more orderly again. Students might even get to know entropy as the “dorm room effect.” • The heat produced by the engine of a car is typically used to heat the car during cold weather. However, is this same heat available in warmer weather? Students are often unaware that their car “heaters” work very well in the summer, too. Just as exercise can warm us when it is cold, the same extra heat is released when we exercise in warm conditions. A car engine in the summer struggles to dissipate heat in the same way that a human struggles to cool off after exercising when the weather is warm. Active Lecture Tips • Challenge your students to come up with examples of common energy conversions in their lives. Have students turn to someone seated near them to find at least two examples. In our daily lives, we rely upon many energy transformations. On our classroom walls, a clock converts electrical energy to mechanical energy to sweep the hands around the clock’s face (unless it is digital!). Our physical (mechanical) activities walking to and from the classroom rely upon the chemical energy from our diet. This chemical energy in our diet also helps us maintain a steady body temperature (heat). • Challenge your students to explain why they feel warm when it is 30C (86F) outside if their core body temperature is 37C (98.6F). Shouldn’t they feel cold? Have students work in groups of two or three to think this through. The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a core body temperature around 37C. Thus, we sweat and behave in ways that help release our extra heat generated in cellular respiration. • See the Activity Keeping an Organized Dorm Room Requires Energy, Just Like in a Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. • See the Activity Universal Currency in the Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 50

Kinetic energy of movement
Figure Fuel Energy conversion Waste products Heat energy Gasoline Carbon dioxide + + Combustion Kinetic energy of movement Oxygen Water Energy conversion in a car Heat energy Cellular respiration Figure Energy transformations in a car and a cell Glucose Carbon dioxide + + ATP ATP Oxygen Water Energy for cellular work Energy conversion in a cell

Chemical reactions either release or store energy
release energy (exergonic reactions) or require an input of energy and store energy (endergonic reactions). Student Misconceptions and Concerns • Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy. They also may not have distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. • All too often we hear or read that some thing or reaction creates energy. We might hear or read that a power plant “produces” energy or that mitochondria “make” energy. Even in our classroom conversations, we may occasionally slip into this error. When discussing the first law of thermodynamics, consider emphasizing the inaccuracy of such statements. • Although typically familiar with the concept of dietary calories, students often struggle to think of calories as a source of potential energy. For many students, it is not clear that potential energy is stored in food as calories. Teaching Tips • The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) as an equivalent mass of protein or carbohydrates (about 4.5–5 kcal per gram). Thus, when comparing equal masses of fat, protein, and lipid, the fat has nearly twice the potential energy. Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 lb overweight, you would be nearly 40 lb overweight if the same energy were stored as carbohydrates or proteins instead of fat.) • The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon the size and activity of a person, a human might burn 2,000 dietary calories (kilocalories) a day. This is enough energy to raise the temperature of 20 liters of liquid water from 0 to 100C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100C, but it takes much more energy to melt ice or to convert boiling water into steam.) 52

Exergonic reactions release energy.
These reactions release the energy in covalent bonds of the reactants. Burning wood releases the energy in glucose as heat and light. Cellular respiration involves many steps, releases energy slowly, and uses some of the released energy to produce ATP. Student Misconceptions and Concerns • Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy. They also may not have distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. • All too often we hear or read that some thing or reaction creates energy. We might hear or read that a power plant “produces” energy or that mitochondria “make” energy. Even in our classroom conversations, we may occasionally slip into this error. When discussing the first law of thermodynamics, consider emphasizing the inaccuracy of such statements. • Although typically familiar with the concept of dietary calories, students often struggle to think of calories as a source of potential energy. For many students, it is not clear that potential energy is stored in food as calories. Teaching Tips • The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) as an equivalent mass of protein or carbohydrates (about 4.5–5 kcal per gram). Thus, when comparing equal masses of fat, protein, and lipid, the fat has nearly twice the potential energy. Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 lb overweight, you would be nearly 40 lb overweight if the same energy were stored as carbohydrates or proteins instead of fat.) • The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon the size and activity of a person, a human might burn 2,000 dietary calories (kilocalories) a day. This is enough energy to raise the temperature of 20 liters of liquid water from 0 to 100C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100C, but it takes much more energy to melt ice or to convert boiling water into steam.) 53

Amount of energy released
Reactants Amount of energy released Energy Products Potential energy Figure 5.11a Exergonic reaction, energy released

An endergonic reaction
requires an input of energy and yields products rich in potential energy. Endergonic reactions start with reactant molecules that contain relatively little potential energy but end with products that contain more chemical energy. Student Misconceptions and Concerns • Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy. They also may not have distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. • All too often we hear or read that some thing or reaction creates energy. We might hear or read that a power plant “produces” energy or that mitochondria “make” energy. Even in our classroom conversations, we may occasionally slip into this error. When discussing the first law of thermodynamics, consider emphasizing the inaccuracy of such statements. • Although typically familiar with the concept of dietary calories, students often struggle to think of calories as a source of potential energy. For many students, it is not clear that potential energy is stored in food as calories. Teaching Tips • The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) as an equivalent mass of protein or carbohydrates (about 4.5–5 kcal per gram). Thus, when comparing equal masses of fat, protein, and lipid, the fat has nearly twice the potential energy. Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 lb overweight, you would be nearly 40 lb overweight if the same energy were stored as carbohydrates or proteins instead of fat.) • The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon the size and activity of a person, a human might burn 2,000 dietary calories (kilocalories) a day. This is enough energy to raise the temperature of 20 liters of liquid water from 0 to 100C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100C, but it takes much more energy to melt ice or to convert boiling water into steam.) 55

Amount of energy required
Figure 5.11b Products Energy Amount of energy required Reactants Potential energy Figure 5.11b Endergonic reaction, energy required

Photosynthesis is a type of endergonic process. In photosynthesis,
energy-poor reactants (carbon dioxide and water) are used, energy is absorbed from sunlight, and energy-rich sugar molecules are produced. Student Misconceptions and Concerns • Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy. They also may not have distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. • All too often we hear or read that some thing or reaction creates energy. We might hear or read that a power plant “produces” energy or that mitochondria “make” energy. Even in our classroom conversations, we may occasionally slip into this error. When discussing the first law of thermodynamics, consider emphasizing the inaccuracy of such statements. • Although typically familiar with the concept of dietary calories, students often struggle to think of calories as a source of potential energy. For many students, it is not clear that potential energy is stored in food as calories. Teaching Tips • The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) as an equivalent mass of protein or carbohydrates (about 4.5–5 kcal per gram). Thus, when comparing equal masses of fat, protein, and lipid, the fat has nearly twice the potential energy. Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 lb overweight, you would be nearly 40 lb overweight if the same energy were stored as carbohydrates or proteins instead of fat.) • The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon the size and activity of a person, a human might burn 2,000 dietary calories (kilocalories) a day. This is enough energy to raise the temperature of 20 liters of liquid water from 0 to 100C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100C, but it takes much more energy to melt ice or to convert boiling water into steam.) 57

Chemical reactions either release or store energy
A living organism carries out thousands of endergonic and exergonic chemical reactions. The total of an organism’s chemical reactions is called metabolism. A metabolic pathway is a series of chemical reactions that either builds a complex molecule or breaks down a complex molecule into simpler compounds. Student Misconceptions and Concerns • Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy. They also may not have distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. • All too often we hear or read that some thing or reaction creates energy. We might hear or read that a power plant “produces” energy or that mitochondria “make” energy. Even in our classroom conversations, we may occasionally slip into this error. When discussing the first law of thermodynamics, consider emphasizing the inaccuracy of such statements. • Although typically familiar with the concept of dietary calories, students often struggle to think of calories as a source of potential energy. For many students, it is not clear that potential energy is stored in food as calories. Teaching Tips • The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) as an equivalent mass of protein or carbohydrates (about 4.5–5 kcal per gram). Thus, when comparing equal masses of fat, protein, and lipid, the fat has nearly twice the potential energy. Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 lb overweight, you would be nearly 40 lb overweight if the same energy were stored as carbohydrates or proteins instead of fat.) • The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon the size and activity of a person, a human might burn 2,000 dietary calories (kilocalories) a day. This is enough energy to raise the temperature of 20 liters of liquid water from 0 to 100C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100C, but it takes much more energy to melt ice or to convert boiling water into steam.) 58

Energy coupling uses the energy released from exergonic reactions to drive endergonic reactions, typically using the energy stored in ATP molecules. Student Misconceptions and Concerns • Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy. They also may not have distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. • All too often we hear or read that some thing or reaction creates energy. We might hear or read that a power plant “produces” energy or that mitochondria “make” energy. Even in our classroom conversations, we may occasionally slip into this error. When discussing the first law of thermodynamics, consider emphasizing the inaccuracy of such statements. • Although typically familiar with the concept of dietary calories, students often struggle to think of calories as a source of potential energy. For many students, it is not clear that potential energy is stored in food as calories. Teaching Tips • The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) as an equivalent mass of protein or carbohydrates (about 4.5–5 kcal per gram). Thus, when comparing equal masses of fat, protein, and lipid, the fat has nearly twice the potential energy. Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 lb overweight, you would be nearly 40 lb overweight if the same energy were stored as carbohydrates or proteins instead of fat.) • The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon the size and activity of a person, a human might burn 2,000 dietary calories (kilocalories) a day. This is enough energy to raise the temperature of 20 liters of liquid water from 0 to 100C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100C, but it takes much more energy to melt ice or to convert boiling water into steam.) 59

ATP drives cellular work by coupling exergonic and endergonic reactions
ATP, adenosine triphosphate, powers nearly all forms of cellular work. ATP consists of adenosine and a triphosphate tail of three phosphate groups. Student Misconceptions and Concerns • Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy. They also may not have distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. • Energy coupling at the cellular level may be new to many students, but it is a familiar concept when related to the use of money in our society. Students might be discouraged if the only benefit of work was the ability to make purchases from the employer. (We all might soon tire of a fast-food job that only paid its employees in food!) Money permits the coupling of a generation of value (a paycheck, analogous to an energy-releasing reaction) to an energy-consuming reaction (money, which allows us to make purchases in distant locations). This idea of earning and spending is a common concept we all know well. Teaching Tips • The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon the size and activity of a person, a human might burn 2,000 dietary calories (kilocalories) a day. This is enough energy to raise the temperature of 20 liters of liquid water from 0 to 100C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100C, but it takes much more energy to melt ice or to convert boiling water into steam.) • When introducing ATP and ADP, consider asking your students to think of the terms as A-3-P and A-2-P, noting that the word roots “tri” = 3 and “di” = 2. It might help students to keep track of the number of phosphates more easily. • Recycling is essential in cell biology. Damaged organelles are broken down intracellularly, and chemical components, the monomers of the cytoskeleton, and ADP are routinely recycled. There are several advantages common to human recycling of garbage and cellular recycling. Both save energy by avoiding the need to remanufacture the basic units, and both avoid an accumulation of waste products that could interfere with other “environmental” chemistry (the environment of the cell or the environment of the human population). 60

Hydrolysis of ATP releases energy by transferring its third phosphate from ATP to some other molecule in a process called phosphorylation. Most cellular work depends on ATP energizing molecules by phosphorylating them. Student Misconceptions and Concerns • Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy. They also may not have distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. • Energy coupling at the cellular level may be new to many students, but it is a familiar concept when related to the use of money in our society. Students might be discouraged if the only benefit of work was the ability to make purchases from the employer. (We all might soon tire of a fast-food job that only paid its employees in food!) Money permits the coupling of a generation of value (a paycheck, analogous to an energy-releasing reaction) to an energy-consuming reaction (money, which allows us to make purchases in distant locations). This idea of earning and spending is a common concept we all know well. Teaching Tips • The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon the size and activity of a person, a human might burn 2,000 dietary calories (kilocalories) a day. This is enough energy to raise the temperature of 20 liters of liquid water from 0 to 100C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100C, but it takes much more energy to melt ice or to convert boiling water into steam.) • When introducing ATP and ADP, consider asking your students to think of the terms as A-3-P and A-2-P, noting that the word roots “tri” = 3 and “di” = 2. It might help students to keep track of the number of phosphates more easily. • Recycling is essential in cell biology. Damaged organelles are broken down intracellularly, and chemical components, the monomers of the cytoskeleton, and ADP are routinely recycled. There are several advantages common to human recycling of garbage and cellular recycling. Both save energy by avoiding the need to remanufacture the basic units, and both avoid an accumulation of waste products that could interfere with other “environmental” chemistry (the environment of the cell or the environment of the human population). 61

Triphosphate Adenosine P P P ATP
Figure 5.12a-1 The hydrolysis of ATP yielding ADP, a phosphate group, and energy (step 1)

Triphosphate Adenosine P P P ATP H2O Diphosphate Adenosine P P P
Energy Figure 5.12a-2 The hydrolysis of ATP yielding ADP, a phosphate group, and energy (step 2) Phosphate ADP

There are three main types of cellular work:
chemical, mechanical, and transport. ATP drives all three of these types of work. Student Misconceptions and Concerns • Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy. They also may not have distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. • Energy coupling at the cellular level may be new to many students, but it is a familiar concept when related to the use of money in our society. Students might be discouraged if the only benefit of work was the ability to make purchases from the employer. (We all might soon tire of a fast-food job that only paid its employees in food!) Money permits the coupling of a generation of value (a paycheck, analogous to an energy-releasing reaction) to an energy-consuming reaction (money, which allows us to make purchases in distant locations). This idea of earning and spending is a common concept we all know well. Teaching Tips • The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon the size and activity of a person, a human might burn 2,000 dietary calories (kilocalories) a day. This is enough energy to raise the temperature of 20 liters of liquid water from 0 to 100C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100C, but it takes much more energy to melt ice or to convert boiling water into steam.) • When introducing ATP and ADP, consider asking your students to think of the terms as A-3-P and A-2-P, noting that the word roots “tri” = 3 and “di” = 2. It might help students to keep track of the number of phosphates more easily. • Recycling is essential in cell biology. Damaged organelles are broken down intracellularly, and chemical components, the monomers of the cytoskeleton, and ADP are routinely recycled. There are several advantages common to human recycling of garbage and cellular recycling. Both save energy by avoiding the need to remanufacture the basic units, and both avoid an accumulation of waste products that could interfere with other “environmental” chemistry (the environment of the cell or the environment of the human population). 64

Protein filament moved
Chemical work P ATP P ADP + P Reactants Product formed Transport work ATP ADP + P P P Transport protein Solute transported Figure 5.12b How ATP powers cellular work Mechanical work ATP P ADP + P P Motor protein Protein filament moved

A cell uses and regenerates ATP continuously.
In the ATP cycle, energy released in an exergonic reaction, such as the breakdown of glucose during cellular respiration, is used in an endergonic reaction to generate ATP from ADP. Student Misconceptions and Concerns • Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy. They also may not have distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. • Energy coupling at the cellular level may be new to many students, but it is a familiar concept when related to the use of money in our society. Students might be discouraged if the only benefit of work was the ability to make purchases from the employer. (We all might soon tire of a fast-food job that only paid its employees in food!) Money permits the coupling of a generation of value (a paycheck, analogous to an energy-releasing reaction) to an energy-consuming reaction (money, which allows us to make purchases in distant locations). This idea of earning and spending is a common concept we all know well. Teaching Tips • The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon the size and activity of a person, a human might burn 2,000 dietary calories (kilocalories) a day. This is enough energy to raise the temperature of 20 liters of liquid water from 0 to 100C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100C, but it takes much more energy to melt ice or to convert boiling water into steam.) • When introducing ATP and ADP, consider asking your students to think of the terms as A-3-P and A-2-P, noting that the word roots “tri” = 3 and “di” = 2. It might help students to keep track of the number of phosphates more easily. • Recycling is essential in cell biology. Damaged organelles are broken down intracellularly, and chemical components, the monomers of the cytoskeleton, and ADP are routinely recycled. There are several advantages common to human recycling of garbage and cellular recycling. Both save energy by avoiding the need to remanufacture the basic units, and both avoid an accumulation of waste products that could interfere with other “environmental” chemistry (the environment of the cell or the environment of the human population). 66

ATP synthesis is endergonic ATP ATP hydrolysis is exergonic
Figure 5.12c ATP synthesis is endergonic ATP ATP hydrolysis is exergonic Energy from cellular respiration (exergonic) Energy for cellular work (endergonic) Figure 5.12c The ATP cycle ADP + P

How Enzymes Function 68

Enzymes speed up the cell’s chemical reactions by lowering energy barriers
Although biological molecules possess much potential energy, it is not released spontaneously. An energy barrier must be overcome before a chemical reaction can begin. This energy is called the activation energy (because it activates the reactants). Student Misconceptions and Concerns • For students not previously familiar with activation energy, analogies can make all the difference. Activation energy can be thought of as a small input that is needed to trigger a large output. This is like (a) an irritated person who needs only a bit more frustration to explode in anger, (b) small waves that lift debris over a dam, or (c) lighting a match around lighter fluid. In each situation, the output is much greater than the input. Teaching Tips • The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out, that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids. 69

We can think of activation energy as the amount of energy needed for a reactant molecule to move “uphill” to a higher-energy but an unstable state so that the “downhill” part of the reaction can begin. One way to speed up a reaction is to add heat, which agitates atoms so that bonds break more easily and reactions can proceed, but too much heat will kill a cell. Student Misconceptions and Concerns • For students not previously familiar with activation energy, analogies can make all the difference. Activation energy can be thought of as a small input that is needed to trigger a large output. This is like (a) an irritated person who needs only a bit more frustration to explode in anger, (b) small waves that lift debris over a dam, or (c) lighting a match around lighter fluid. In each situation, the output is much greater than the input. Teaching Tips • The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out, that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids. 70

Enzymes function as biological catalysts, increase the rate of a reaction without being consumed by the reaction, and are usually proteins (although some RNA molecules can function as enzymes). Enzymes speed up a reaction by lowering the activation energy needed for a reaction to begin. Student Misconceptions and Concerns • For students not previously familiar with activation energy, analogies can make all the difference. Activation energy can be thought of as a small input that is needed to trigger a large output. This is like (a) an irritated person who needs only a bit more frustration to explode in anger, (b) small waves that lift debris over a dam, or (c) lighting a match around lighter fluid. In each situation, the output is much greater than the input. Teaching Tips • The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out, that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids. 71

Activation energy barrier
Figure Activation energy barrier Reactant Energy Figure The effect of an enzyme in lowering the activation energy (part 2) Products Without enzyme

Activation energy barrier reduced by enzyme
Figure Enzyme Activation energy barrier reduced by enzyme Reactant Energy Figure The effect of an enzyme in lowering the activation energy (part 3) Products With enzyme

Progress of the reaction
b Reactants Energy c Figure The effect of an enzyme in lowering the activation energy (part 4) Products Progress of the reaction

A specific enzyme catalyzes each cellular reaction
An enzyme is very selective in the reaction it catalyzes and has a shape that determines the enzyme’s specificity. The specific reactant that an enzyme acts on is called the enzyme’s substrate. A substrate fits into a region of the enzyme called the active site. Enzymes are specific because only specific substrate molecules fit into their active site. Student Misconceptions and Concerns • The specific interactions of enzymes and substrates can be illustrated with simple physical models. Many students new to these concepts will benefit from several forms of explanation, including diagrams such as those in the textbook, physical models, and the opportunity to manipulate or create their own examples. Just like pitching a tent, new concepts are best constructed with many lines of support. Teaching Tips • The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out, that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids. • The text notes that the relationship between an enzyme and its substrate is like a handshake, with each hand generally conforming to the shape of the other. This induced fit is also like the change in shape of a glove when a hand is inserted. The glove’s general shape matches the hand, but the final “fit” requires some additional adjustments. Active Lecture Tips • See the Activity Students, Design Your Own Enzyme-Catalyzed Reaction on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc. 75

A specific enzyme catalyzes each cellular reaction
The following figure illustrates the catalytic cycle of an enzyme. Student Misconceptions and Concerns • The specific interactions of enzymes and substrates can be illustrated with simple physical models. Many students new to these concepts will benefit from several forms of explanation, including diagrams such as those in the textbook, physical models, and the opportunity to manipulate or create their own examples. Just like pitching a tent, new concepts are best constructed with many lines of support. Teaching Tips • The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out, that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids. • The text notes that the relationship between an enzyme and its substrate is like a handshake, with each hand generally conforming to the shape of the other. This induced fit is also like the change in shape of a glove when a hand is inserted. The glove’s general shape matches the hand, but the final “fit” requires some additional adjustments. Active Lecture Tips • See the Activity Students, Design Your Own Enzyme-Catalyzed Reaction on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 76

The enzyme available with an empty active site
Figure 1 The enzyme available with an empty active site Active site Enzyme (sucrase) Figure The catalytic cycle of an enzyme (step 1)

Figure 1 The enzyme available with an empty active site Substrate (sucrose) Active site 2 Substrate binds to enzyme with induced fit. Enzyme (sucrase) Figure The catalytic cycle of an enzyme (step 2)

Figure 1 The enzyme available with an empty active site Substrate (sucrose) Active site 2 Substrate binds to enzyme with induced fit. Enzyme (sucrase) H2O Figure The catalytic cycle of an enzyme (step 3) 3 The substrate is converted to products

Figure 1 The enzyme available with an empty active site Substrate (sucrose) Active site 2 Substrate binds to enzyme with induced fit. Enzyme (sucrase) Glucose Fructose H2O Figure The catalytic cycle of an enzyme (step 4) 4 The products are released 3 The substrate is converted to products

Temperature affects molecular motion.
For every enzyme, there are optimal conditions under which it is most effective. Temperature affects molecular motion. An enzyme’s optimal temperature produces the highest rate of contact between the reactants and the enzyme’s active site. Most human enzymes work best at 35–40°C. The optimal pH for most enzymes is near neutrality. Student Misconceptions and Concerns • The specific interactions of enzymes and substrates can be illustrated with simple physical models. Many students new to these concepts will benefit from several forms of explanation, including diagrams such as those in the textbook, physical models, and the opportunity to manipulate or create their own examples. Just like pitching a tent, new concepts are best constructed with many lines of support. Teaching Tips • The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out, that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids. • The text notes that the relationship between an enzyme and its substrate is like a handshake, with each hand generally conforming to the shape of the other. This induced fit is also like the change in shape of a glove when a hand is inserted. The glove’s general shape matches the hand, but the final “fit” requires some additional adjustments. Active Lecture Tips • See the Activity Students, Design Your Own Enzyme-Catalyzed Reaction on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 81

Many enzymes require nonprotein helpers called cofactors, which
bind to the active site and function in catalysis. Some cofactors are inorganic, such as the ions of zinc, iron, or copper. If a cofactor is an organic molecule, such as most vitamins, it is called a coenzyme. Student Misconceptions and Concerns • The specific interactions of enzymes and substrates can be illustrated with simple physical models. Many students new to these concepts will benefit from several forms of explanation, including diagrams such as those in the textbook, physical models, and the opportunity to manipulate or create their own examples. Just like pitching a tent, new concepts are best constructed with many lines of support. Teaching Tips • The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out, that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids. • The text notes that the relationship between an enzyme and its substrate is like a handshake, with each hand generally conforming to the shape of the other. This induced fit is also like the change in shape of a glove when a hand is inserted. The glove’s general shape matches the hand, but the final “fit” requires some additional adjustments. Active Lecture Tips • See the Activity Students, Design Your Own Enzyme-Catalyzed Reaction on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 82

Enzyme inhibition can regulate enzyme activity in a cell
A chemical that interferes with an enzyme’s activity is called an inhibitor. Competitive inhibitors block substrates from entering the active site and reduce an enzyme’s productivity. Student Misconceptions and Concerns The specific interactions of enzymes and substrates can be illustrated with simple physical models. Many students new to these concepts will benefit from several forms of explanation, including diagrams such as those in the textbook, physical models, and the opportunity to manipulate or create their own examples. Just like pitching a tent, new concepts are best constructed with many lines of support. Teaching Tips • The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out, that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids. • Enzyme inhibitors that block the active site are like (a) a person sitting in your assigned theater seat or (b) a car parked in your parking space. Analogies for inhibitors that change the shape of the active site are more difficult to imagine. Consider challenging your students to think of such analogies. (Perhaps someone adjusting the driver seat of the car differently from your preferences and then leaving it that way when you try to use the car.) • Feedback inhibition relies upon the negative feedback of the accumulation of a product. Ask students in class to suggest other products of reactions that inhibit the process that made them when the product reaches high enough levels. (Gas station pumps routinely shut off when a high level of gasoline is detected. Furnaces typically turn off when enough heat has been produced.) 83

Noncompetitive inhibitors
bind to the enzyme somewhere other than the active site, change the shape of the active site, and prevent the substrate from binding. Student Misconceptions and Concerns The specific interactions of enzymes and substrates can be illustrated with simple physical models. Many students new to these concepts will benefit from several forms of explanation, including diagrams such as those in the textbook, physical models, and the opportunity to manipulate or create their own examples. Just like pitching a tent, new concepts are best constructed with many lines of support. Teaching Tips • The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out, that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids. • Enzyme inhibitors that block the active site are like (a) a person sitting in your assigned theater seat or (b) a car parked in your parking space. Analogies for inhibitors that change the shape of the active site are more difficult to imagine. Consider challenging your students to think of such analogies. (Perhaps someone adjusting the driver seat of the car differently from your preferences and then leaving it that way when you try to use the car.) • Feedback inhibition relies upon the negative feedback of the accumulation of a product. Ask students in class to suggest other products of reactions that inhibit the process that made them when the product reaches high enough levels. (Gas station pumps routinely shut off when a high level of gasoline is detected. Furnaces typically turn off when enough heat has been produced.) 84

Normal binding of substrate
Figure 5.15a Substrate Active site Enzyme Normal binding of substrate Competitive inhibitor Noncompetitive inhibitor Figure 5.15a How inhibitors interfere with substrate binding Enzyme inhibition

PABA is necessary for bacteria in producing Folic Acid
PABA is necessary for bacteria in producing Folic Acid. Humans get their Folic acid as a dietary Vitamin B9. Sulfanilamide blocks the bacterial enzymes that convert PABA to folic acid thus killing them. The Medical use of Sulfanilamide was discovered in 1935 and was awarded the Nobel Prize in 1939 to Gerhard Domagk

Enzyme inhibition can regulate enzyme activity in a cell
Enzyme inhibitors are important in regulating cell metabolism. In some reactions, the product may act as an inhibitor of one of the enzymes in the pathway that produced it. This is called feedback inhibition. Student Misconceptions and Concerns The specific interactions of enzymes and substrates can be illustrated with simple physical models. Many students new to these concepts will benefit from several forms of explanation, including diagrams such as those in the textbook, physical models, and the opportunity to manipulate or create their own examples. Just like pitching a tent, new concepts are best constructed with many lines of support. Teaching Tips • The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out, that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids. • Enzyme inhibitors that block the active site are like (a) a person sitting in your assigned theater seat or (b) a car parked in your parking space. Analogies for inhibitors that change the shape of the active site are more difficult to imagine. Consider challenging your students to think of such analogies. (Perhaps someone adjusting the driver seat of the car differently from your preferences and then leaving it that way when you try to use the car.) • Feedback inhibition relies upon the negative feedback of the accumulation of a product. Ask students in class to suggest other products of reactions that inhibit the process that made them when the product reaches high enough levels. (Gas station pumps routinely shut off when a high level of gasoline is detected. Furnaces typically turn off when enough heat has been produced.) © 2015 Pearson Education, Inc. 87

– Feedback inhibition Enzyme 1 Enzyme 2 Enzyme 3 A B C D Reaction 1
Figure 5.15b – Feedback inhibition Enzyme 1 Enzyme 2 Enzyme 3 A B C D Reaction 1 Reaction 2 Reaction 3 Starting molecule Product Figure 5.15b Feedback inhibition of a metabolic pathway in which product D acts as an inhibitor of enzyme 1

Many drugs, pesticides, and poisons are enzyme inhibitors
Many beneficial drugs act as enzyme inhibitors, including ibuprofen, which inhibits an enzyme involved in the production of prostaglandins (messenger molecules that increase the sensation of pain and inflammation), some blood pressure medicines, some antidepressants, many antibiotics, and protease inhibitors used to fight HIV. Teaching Tips Challenge your class to identify advantages of specific enzyme inhibitors for pest control. These advantages include (a) the ability to target chemical reactions of only certain types of pest organisms and (b) the ability to target chemical reactions that are found in insects but not in humans. © 2015 Pearson Education, Inc. 89

Enzyme inhibitors have also been developed as
pesticides and deadly poisons for chemical warfare. Teaching Tips Challenge your class to identify advantages of specific enzyme inhibitors for pest control. These advantages include (a) the ability to target chemical reactions of only certain types of pest organisms and (b) the ability to target chemical reactions that are found in insects but not in humans. 90

REVIEW 91

You should now be able to
Describe the fluid mosaic structure of cell membranes. Describe the diverse functions of membrane proteins. Relate the structure of phospholipid molecules to the structure and properties of cell membranes. Define diffusion and describe the process of passive transport. © 2015 Pearson Education, Inc. 92

Explain how osmosis can be defined as the diffusion of water across a membrane. Distinguish between hypertonic, hypotonic, and isotonic solutions. Explain how transport proteins facilitate diffusion. Distinguish between exocytosis, endocytosis, phagocytosis, and receptor-mediated endocytosis. © 2015 Pearson Education, Inc. 93

Define and compare kinetic energy, potential energy, chemical energy, and heat. Define the two laws of thermodynamics and explain how they relate to biological systems. Define and compare endergonic and exergonic reactions. Explain how cells use cellular respiration and energy coupling to survive. © 2015 Pearson Education, Inc. 94

Explain how ATP functions as an energy shuttle. Explain how enzymes speed up chemical reactions. Explain how competitive and noncompetitive inhibitors alter an enzyme’s activity. Explain how certain drugs, pesticides, and poisons can affect enzymes. © 2015 Pearson Education, Inc. 95

Passive transport (requires no energy)
Active transport (requires energy) Diffusion Facilitated diffusion Osmosis Higher solute concentration Higher solute concentration Higher free water concentration Solute ATP Water Figure 5.UN01 Review the concepts, 5.8 Lower solute concentration Lower free water concentration Lower solute concentration

Molecules cross cell membranes polar molecules and ions
by by passive transport (a) may be moving down moving against requires ATP (b) uses diffusion (d) uses Figure 5.UN02 Connecting the concepts, question 1 (e) of of polar molecules and ions (c) P

c. b. a. d. f. Figure 5.UN03 Connecting the concepts, question 2 e.

Figure 5.UN05 Testing your knowledge, question 15

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