1. Chapter 5- The Working Cell
BIO 101
Chapter 5- The Working Cell

2. The Working Cell Cells “work”by
Moving substance into and out of the cell.
Doing chemical reactions which utilize enzymes.

3. 5.1 Membranes are fluid mosaics of lipids and proteins with many functions
Figure 5.1 Some functions of membrane proteins
ATP
Glycoprotein
CYTOPLASM 3

4. 5.1 Membranes are fluid mosaics of lipids and proteins with many functions
Membrane proteins perform many functions.
Some proteins help maintain cell shape and coordinate changes inside and outside the cell through their attachment to the cytoskeleton and extracellular matrix.
Some proteins function as receptors for chemical messengers from other cells.
Some membrane proteins function as enzymes.
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 jellybeans 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 jellybeans stuck into the sandwich represent proteins variously embedded partially into or completely through the membrane. Transport proteins would be like the jellybeans 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.)
© 2012 Pearson Education, Inc. 4

5. 5.1 Membranes are fluid mosaics of lipids and proteins with many functions
Some membrane glycoproteins are involved in cell-cell recognition.
Membrane proteins may participate in the intercellular junctions that attach adjacent cells to each other.
Membrane proteins transport substances across the membrane.
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 jellybeans 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 jellybeans stuck into the sandwich represent proteins variously embedded partially into or completely through the membrane. Transport proteins would be like the jellybeans 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.)
© 2012 Pearson Education, Inc. 5

6. 5.2 EVOLUTION CONNECTION: Membranes form spontaneously, 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. 6

7. Types of transportation possible across membrane….
Diffusion-
Simple diffusion-
Osmosis-
Facilitated Diffusion-
Active Transport-
Bulk Flow/Exocytosis/Endocytosis-

8. Molecules of dye Membrane Pores Net diffusion Net diffusion
Figure 5.3A
Molecules of dye
Membrane
Pores
Figure 5.3A Passive transport of one type of molecule
Net diffusion
Net diffusion
Equilibrium 8

9. Diffusion-overview Substances move down the concentration gradient
Passive, requires no energy
Speed dependent on:
Concentration difference, steepness
Temperature
Size of molecules
Presence of electric charge
Pressure

10. 5.4 Osmosis is the diffusion of water across a membrane
One of the most important substances that crosses membranes 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 their lives when they 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.
© 2012 Pearson Education, Inc. 10

11. Lower concentration of solute Higher concentration of solute
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 11

12. 5.5 Water balance between cells and their surroundings is crucial to organisms
Tonicity is a term that describes the ability of a solution to cause a cell to gain or lose water.
Tonicity mostly depends on the concentration of a solute on both sides of the membrane.
Hypotonic- _______________
Hypertonic- _______________
Isotonic- __________________
Student Misconceptions and Concerns
Students easily confuse the term hypertonic and hypotonic. One challenge is to get them 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
1. 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).
2. 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)
3. 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.
© 2012 Pearson Education, Inc. 12

13. 5.5 Water balance between cells and their surroundings is crucial to organisms
RBC
Most animal cells lack the ability to prevent lysis if placed in a hypotonic solution.
Human cells are about 0.9% saline (salt water).
So cells are isotonic to a 0.9% saline solution. Ocean water is about 3.5 % salt.
SO…now you know why you can’t drink salt water!

14. 1 liter of distilled water
2% sucrose solution
1 liter of
10% sucrose solution
1 liter of
2% sucrose solution
1 liter of distilled water
Hypotonic
Conditions
Hypertonic
Conditions
Isotonic
Conditions

15. 5.5 Water balance between cells and their surroundings is crucial to organisms
For an animal cell to survive in a hypotonic or hypertonic environment, it must engage in osmoregulation, the control of water balance.
The cell walls of plant cells, prokaryotes, and fungi make water balance issues somewhat different.
The cell wall prevents the cell from taking in too much water but pressure builds up! This is called turgor pressure.
Student Misconceptions and Concerns
Students easily confuse the term hypertonic and hypotonic. One challenge is to get them 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
1. 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).
2. 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)
3. 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.
© 2012 Pearson Education, Inc. 15

16. Turgor Pressure

17. 5.6 Transport proteins can facilitate diffusion across membranes
Solute molecule
Membrane proteins can be channels or carriers (facilitated diffusion)
Figure 5.6 Transport protein providing a channel for the diffusion of a specific solute across a membrane
Transport protein 17

18. Example of
Facilitative Diffusion:
glucose transporter (channel)

19. 5.7 SCIENTIFIC DISCOVERY: Research on another membrane protein led to the discovery of aquaporins
Dr. Peter Agre received the 2003 Nobel Prize in chemistry for his discovery of aquaporins.
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.
His research on the Rh protein used in blood typing led to this discovery.
Teaching Tips
The functional significance of aquaporins in cell membranes is somewhat like open windows in a home. Even without windows, air moves slowly into and out of a home. Open windows and aquaporins facilitate the process of these movements, speeding them up.
© 2012 Pearson Education, Inc. 19

20. 5.8 Cells expend energy in the active transport of a solute
Transport protein P P
Protein changes shape.
Phosphate detaches. P
ATP
Solute
ADP
Figure 5.8_s4 Active transport of a solute across a membrane (step 4) 1
Solute binding 2
Phosphate attaching 3
Transport 4
Protein reversion 20

21. Example of Active Transport:
Calcium Pump

22. Moves 2 kinds of ions in opposite directions. Requires ATP
3 Na+ move out of cell, 2 K+ ions move in
Important in nerve cell impulse transmission
Example of
ActiveTransport/
Pump/Cotransport:
Sodium-Potassium Pump

23. Move in response to gradient
Uses energy to move against gradient
High
Concentration
gradient across
cell membrane
ATP
Low
SimpleDiffusion
of lipid-soluble
Substances
across bilayer
Passive transport of water-
soluble substances
through channel protein;
no energy input needed
Active transport
through ATPase;
requires energy
input from ATP
aka Facilitated Diffusion

24. 5.9 Exocytosis and endocytosis transport large molecules across membranes
There are three kinds of endocytosis.
Phagocytosis
Pinocytosis
Receptor-mediated endocytosis
Teaching Tips
Students carefully considering exocytosis may notice that membrane from secretory vesicles is added to the plasma membrane. Consider challenging your students 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.)
© 2012 Pearson Education, Inc. 24

25. Endocytosis (vesicles in)
Exocytosis (vesicles out)

26. Receptor-mediated Endocytosis

27. Type of WBC, defensive function
parasite
macrophage

28. Type of Transport Simple Diffusion Osmosis Facilitated Active
Passive or Energy
Concentration Gradient
Membrane Protein
Phospho-lipids
Examples
Simple
Diffusion
Osmosis
Facilitated
Active
Transport
Exo/Endo-
cytosis

29. Membrane Cycling
Proteins that will become part of the cell membrane are shipped in vesicles that fuse with the Golgi body. They are modified and sent off in other vesicles that fuse with the plasma membrane. In this way the cell membrane can be replaced and repaired as needed.

30. Why is movement across a membrane important?
Cells need raw materials
_____________________
Cells need to get rid of waste:
____________________
Cells need to maintain water balance:
__________________________
___________________

31. Cystic Fibrosis CFTR is a protein channel which allow
for the movement of Cl-,
followed by water
Thin, slippery film is
produced on surface of cell/tissue
Single amino acid change in
protein causes the CFTR to be
destroyed before reaching cell membrane
No film causes mucus to dry out and become sticky

32. Internet sites
Diffusion, Osmosis, and Movement Across a Membrane:

33. The Working Cell Cells “work”by
Moving substance into and out of the cell.
Doing chemical reactions which utilize enzymes.

34. Energy Flows
Energy is not created or destroyed, there is a finite amount of energy in the universe
(1st law of thermodynamics)
Energy is converted from one form to another. It flows in one direction, spontaneously, from a concentrated (ordered) form to a less concentrated form. Energy disperses.
(2nd law of thermodynamics)
Example: photosynthesis converts solar energy to chemical energy

35. 5.10 Cells transform energy as they perform work
Cells are small units, a chemical factory, housing thousands of chemical reactions.
Cells use these chemical reactions for
cell maintenance,
manufacture of cellular parts, and
cell replication.
Student Misconceptions and Concerns
Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy or distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples.
Teaching Tips
1. 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). Consider challenging your students to come up with additional examples of such common energy conversions in their lives.
2. Some students can relate well to the concept of entropy as applied to the room where they live. Despite their 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.”
3. 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 weather is warm.
4. Here is a question that might make cellular respiration a little more meaningful to your students. Ask your students 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? 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.
© 2012 Pearson Education, Inc. 35

36. 5.10 Cells transform energy as they perform work
Energy is the capacity to cause change or to perform work.
There are two kinds of energy.
Kinetic energy is the energy of motion.
Potential energy is energy that matter possesses or stores 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 or distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples.
Teaching Tips
1. 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). Consider challenging your students to come up with additional examples of such common energy conversions in their lives.
2. Some students can relate well to the concept of entropy as applied to the room where they live. Despite their 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.”
3. 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 weather is warm.
4. Here is a question that might make cellular respiration a little more meaningful to your students. Ask your students 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? 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.
© 2012 Pearson Education, Inc. 36

37. Kinetic energy of movement
Figure 5.10
Fuel
Energy conversion
Waste products
Heat energy
Carbon dioxide
Gasoline  
Combustion
Kinetic energy of movement
Oxygen
Water
Energy conversion in a car
Heat energy
Figure 5.10 Energy transformations in a car and a cell
Cellular respiration
Glucose
Carbon dioxide  
ATP
ATP
Oxygen
Energy for cellular work
Water
Energy conversion in a cell 37

38. 5.10 Cells transform energy as they perform work
Chemical reactions are either:
Endergonic
Requires input of energy
Products are high in potential energy
Ex. Photosynthesis
Exergonic
Releases energy
More energy in reactants than products
Ex. Cellular Respiration

39. 5.11 Chemical reactions either release or store energy
Photosynthesis is a type of endergonic process.
Energy-poor reactants, carbon dioxide, and water are used.
Energy is absorbed from sunlight.
Energy-rich sugar molecules are produced.
Student Misconceptions and Concerns
1. Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy or distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples.
2. 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.
3. 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
1. 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 lbs overweight, you would be nearly 40 lbs overweight if the same energy were stored as carbohydrates or proteins instead of fat).
2. 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.) 39

40. 5.12 ATP drives cellular work by coupling exergonic and endergonic reactions
ATP, adenosine triphosphate, powers nearly all forms of cellular work.
ATP consists of
__________________________,
___________________________,
________________________.
Student Misconceptions and Concerns
1. Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy or distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples.
2. 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
1. 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.)
2. 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.
3. 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).
© 2012 Pearson Education, Inc. 40

41. 5.12 ATP drives cellular work by coupling exergonic and endergonic reactions
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
1. Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy or distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples.
2. 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
1. 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.)
2. 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.
3. 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).
© 2012 Pearson Education, Inc. 41

42. ATP: Adenosine Triphosphate Phosphate group P P P Adenine Ribose H2O
Figure 5.12A_s2
ATP:
Adenosine
Triphosphate
Phosphate group P P P
Adenine
Ribose
H2O
Hydrolysis
Figure 5.12A_s2 The structure and hydrolysis of ATP (step 2) P P P
Energy
ADP:
Adenosine
Diphosphate 42

43. 5.13 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 (EA).
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.
© 2012 Pearson Education, Inc. 43

44. This reaction is binding A and B together
Role of ENZYMES…
ENZYMES ARE PROTEINS
Shape determines function, Specific
Lowers activation energy (energy needed to run a reaction)
Catalysts (make enzymes occur faster, millions of times faster)
Energy “in”
This reaction is binding A and B together
Energy “out”

45. 5.14 A specific enzyme catalyzes each cellular reaction
Larger than substrates ( reactants that bind to the enzyme)
Take reactants apart OR put reactants together

46. Binding of substrate to enzyme is…
Temporary
Weak
Changes the enzyme’s shape very slightly (induced-fit)

47. Enzyme available with empty active site
Figure 5.14_s4 1
Enzyme available with empty active site
Active site
Substrate (sucrose) 2
Substrate binds to enzyme with induced fit
Enzyme (sucrase)
Glucose
Fructose
Figure 5.14_s4 The catalytic cycle of an enzyme (step 4)
H2O 4
Products are released 3
Substrate is converted to products 47

48. 5.14 A specific enzyme catalyzes each cellular reaction
Enzyme activity is affected by:
Temperature pH
Cofactors (inorganic)
Coenzymes (organic)
Competitive inhibitors
Noncompetitive inhibitors
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
1. 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.
2. 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.
© 2012 Pearson Education, Inc. 48

49. 5.15 Enzyme inhibitors can regulate enzyme activity in a cell
Substrate
Active site
Enzyme
Allosteric site
Normal binding of substrate
Competitive inhibitor
Noncompetitive inhibitor
Figure 5.15A How inhibitors interfere with substrate binding
Enzyme inhibition 49

50. 5.15 Enzyme inhibitors can regulate enzyme activity in a cell
Enzyme inhibitors are important in regulating cell metabolism.
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
1. 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.
2. 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.)
3. 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.) 50

51. Enzyme Biology Place Enzyme Catalysis
Enzyme Activity (other useful animations too)

52. You should now be able to
Describe the fluid mosaic structure of cell membranes.
Describe the diverse functions of membrane proteins.
Define diffusion and describe the process of passive transport.
Explain how osmosis can be defined as the diffusion of water across a membrane.
Distinguish between hypertonic, hypotonic, and isotonic solutions.
© 2012 Pearson Education, Inc. 52

53. You should now be able to
Explain how transport proteins facilitate diffusion.
Describe movement of molecules across the membrane by active transport.
Distinguish between exocytosis/endocytosis, phagocytosis/pinocytosis, and receptor-mediated endocytosis.
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.
© 2012 Pearson Education, Inc. 53

54. You should now be able to
Define and compare endergonic and exergonic reactions.
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.
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