1. Chapter 5
The Working Cell

2. Cool “Fires” Attract Mates and Meals
Fireflies use light to send signals to potential mates
Instead of using chemical signals like most other insects

3. The light comes from a set of chemical reactions
That occur in light-producing organs at the rear of the insect
Many of the enzymes that control a firefly's ability to produce light energy from chemical energy are located in membranes.

4. Females of some species
Produce a light pattern that attracts males of other species, which are then eaten by the female

5. 5.1 Energy is the capacity to perform work
ENERGY AND THE CELL
5.1 Energy is the capacity to perform work
Crash Course-Energy
All organisms require energy
Energy is defined as the capacity to do work
Energy is the capacity to rearrange matter.
Energy can only be described and measured by how it affects matter. We can’t see energy.

6. Kinetic energy is the energy of motion
Heat- (thermal energy)-the movement of molecules or atoms in a body of matter.

7. And can be converted to kinetic energy (the energy of a moving object)
Potential energy is stored energy that an object possesses as a result of its location or structure.
And can be converted to kinetic energy (the energy of a moving object)
Figure 5.1A–C

8. Chemical Energy-the potential energy of molecules
Life depends on the fact that energy can be converted from one form to another.
Ex. Glucose molecules provide energy to power the swimming motion of sperm. In this example, the sperm are changing chemical energy into kinetic energy.

9. 5.2 Two laws govern energy transformations
Thermodynamics
Is the study of energy transformations that occur in a collection of matter.
System-the collection of matter under study in thermodynamics
Ex. Single cell or Earth
Surroundings-everything outside the system
A living thing is an open system-it exchanges both energy and matter with its surroundings.

10. The First Law of Thermodynamics
According to the first law of thermodynamics
Energy can be changed from one form to another
Energy cannot be created or destroyed
Figure 5.2A

11. The Second Law of Thermodynamics
States that energy transformations increase disorder or entropy, and some energy is lost as heat
Entropy-the amount of disorder in a system.
Ex. A steer must eat at least 100 pounds of grain to gain less than 10 pounds of muscle tissue.
Crash Course-Entropy
Figure 5.2B

12. Living systems decrease their entropy while increasing the entropy of the universe.
Ex. Protein Synthesis
The more heat released by a reaction, the greater the increase in entropy.

13. Energy transfers possible in living systems:
Light energy to chemical energy (photosynthesis)
Chemical energy to kinetic energy (cellular respiration)
Potential energy to kinetic energy
Light energy to potential energy

14. 5.3 Chemical reactions either store or release energy
Endergonic reactions-absorb energy and yield products rich in potential energy
Ex. The synthesis of glucose from carbon dioxide and water
Products
Amount of energy required
Energy required
Potential energy of molecules
Reactants
Figure 5.3A

15. Exergonic reactions
Release energy and yield products that contain less potential energy than their reactants
Reactants
Amount of energy released
Energy released
Potential energy of molecules
Products
Figure 5.3B

16. Cells carry out thousands of chemical reactions
The sum of which constitutes cellular metabolism
Energy coupling
Uses exergonic reactions to fuel endergonic reactions
When a cell uses chemical energy to perform work, it couples an exergonic reaction with an endergonic reaction.

17. 5.4 ATP shuttles chemical energy and drives cellular work
ATP contains a nitrogenous base called adenine & 3 phosphate groups.
ATP powers nearly all forms of cellular work
Anything that prevents ATP formation will most likely result in cell death.
ATP can be used as the cell's energy currency because endergonic reactions can be fueled by coupling them with the hydrolysis of high-energy phosphate bonds in ATP.

18. The energy in an ATP molecule
Lies in the bonds between its phosphate groups
Adenosine Triphosphate
Adenosine diphosphate
Phosphate groups
H2O P P P P P + P +
Energy
Hydrolysis
Adenine
Ribose
ATP
ADP
Figure 5.4A

19. ATP drives endergonic reactions by phosphorylation
Transferring a phosphate group to make molecules or compounds
ATP
Chemical work
Mechanical work
Transport work
Membrane protein
Solute P +
Motor protein P
Reactants P P P
Product P
Molecule formed
Protein moved
Solute transported
ADP + P
Figure 5.4B

20. 3 Main Types of Cellular Work: (ATP drives all three)
Chemical
Ex. Protein Synthesis
Mechanical
Ex. Muscle contraction
Transport
Ex. Movement of molecules across membranes

21. Cellular work can be sustained
Because ATP is a renewable resource that cells regenerate
ATP
Dehydration
Synthesis
Hydrolysis
Energy from exergonic reactions
Energy for endergonic reactions
ADP + P
Figure 5.4C

22. HOW ENZYMES FUNCTION
5.5 Enzymes speed up the cell’s chemical reactions by lowering energy barriers
Energy of Activation-the amount of energy that reactants must overcome to start a chemical reaction.
An energy barrier prevents the spontaneous decomposition of ATP in the cell.

23. For a chemical reaction to begin
Reactants must absorb some energy, called the energy of activation
EA barrier
Enzyme
Reactants
Products 1 2
Figure 5.5A

24. Enzymes: Are usually proteins
Can decrease the energy of activation needed to begin a reaction
Does not add energy to a cellular reaction; it speeds up a reaction by lowering the activation energy barrier.
Catalyze reactions & lower the activation energy of the reaction
Without enzymes, most metabolic reactions would occur too slowly to sustain life.

25. 5.6 A specific enzyme catalyzes each cellular reaction
Enzymes have unique three-dimensional shapes due to their protein nature
That shape determines which chemical reactions occur in a cell.
That shape does not change after the reaction.

26. Substrate-a specific reactant that an enzyme acts on.
Fits into an active site-the region of an enzyme that attaches to a substrate.
When a substrate binds to an enzyme, the active site changes shape slightly so that it embraces the substrate more snugly. We call this induced fit.

27. The catalytic cycle of an enzyme1
Enzyme available with empty active site
Active site
Substrate (sucrose) 2
Substrate binds to enzyme with induced fit
Enzyme (sucrase)
Glucose
Fructose
H2O 4
Products are released 3
Substrate is converted to products
Figure 5.6

28. 5.7 The cellular environment affects enzyme activity
Some enzymes require:
Nonprotein, inorganic cofactors, such as metal ions
organic molecules called coenzymes, which are usually vitamins.

29. The following can affect the rate of an enzyme-catalyzed reaction:
Heating, inactivates enzymes by changing the enzyme's three-dimensional shape.
The following can affect the rate of an enzyme-catalyzed reaction: 
temperature  
pH  
competitive inhibitors  
noncompetitive inhibitors

30. 5.8 Enzyme inhibitors block enzyme action
Inhibitors interfere with an enzyme’s activity
Competitive inhibitors bind to the active site of the enzyme; noncompetitive inhibitors bind to a different site
Inhibition of an enzyme is irreversible when bonds form between inhibitor and enzyme.

31. Normal binding of substrate
A competitive inhibitor
Takes the place of a substrate in the active site
A noncompetitive inhibitor
Alters an enzyme’s function by changing its shape
Substrate
Active site
Enzyme
Normal binding of substrate
Competitive inhibitor
Noncompetitive inhibitor
Enzyme inhibition
Figure 5.8

32. 5.9 Many poisons, pesticides, and drugs are enzyme inhibitors
CONNECTION
5.9 Many poisons, pesticides, and drugs are enzyme inhibitors

33. MEMBRANE STRUCTURE AND FUNCTION
5.10 Membranes organize the chemical activities of cells
Membranes
Provide structural order for metabolism
Cell Membrane-Hippocamus

34. The plasma membrane of the cell is selectively permeable
Controlling the flow of substances into or out of the cell
Outside of cell
TEM 200,000 
Cytoplasm
Figure 5.10

35. Functions of the Plasma Membrane:
Forms a selective barrier around the cell.
Plays a role in signal transduction.
Has receptors for chemical messages.
Is involved in self-recognition.

36. 5.11 Membrane phospholipids form a bilayer
Have a hydrophilic head and two hydrophobic tails
Are the main structural components of membranes
Sometimes have a kink due
to a double bond with carbon
Hydrophilic head +
CH3
CH2 N
CH3
CH2
CH3
Phosphate group O O P O– O
CH2 CH
CH2 O O C O C O
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
Symbol
CH2 CH
CH2 CH
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH3
CH3
Hydrophobic tails
Figure 5.11A

37. Phospholipids form a two-layer sheet
Called a phospholipid bilayer, with the heads facing outward and the tails facing inward
Water
Hydrophilic heads
Hydrophobic tails
Water
Figure 5.11B

38. 5.12 The membrane is a fluid mosaic of phospholipids and proteins
A membrane is a fluid mosaic which describes the plasma membrane as consisting of individual proteins and phospholipids that can drift in a phospholipid bilayer.
The cholesterol associated with cell membranes helps to stabilize the cell membrane at body temperature.
Figure 5.12

39. Unsaturated lipids have kinks, which make the membrane more fluid by keeping phospholipids from packing tightly together.
Glycoprotein-a protein with attached sugars
Glycolipid-lipid with attached sugars
A major function of glycoproteins and glycolipids in the cell membrane is to allow the cells of an embryo to sort themselves into tissues and organs.

40. Fibers of the extracellular matrix
Carbohydrate (of glycoprotein)
Glycoprotein
Glycolipid
Plasma membrane
Phospholipid
Proteins
Microfilaments of cytoskeleton
Cholesterol
Cytoplasm

41. 5.13 Proteins make the membrane a mosaic of function
Proteins perform most of the functions of a membrane.
Many membrane proteins
Function as enzymes
Provide cellular identification tags
Attach the membrane to the
cytoskeleton.
Figure 5.13A

42. Other membrane proteins
Function as receptors for chemical messages from other cells
Messenger molecule
Receptor
Activated molecule
Figure 5.13B

43. Membrane proteins also function in transport
Moving substances across the membrane
ATP
Figure 5.13C

44. 5.14 Passive transport is diffusion across a membrane
In passive transport, substances diffuse through membranes without work by the cell
Spreading from areas of high concentration to areas of low concentration
Molecules of dye
Membrane
Equilibrium
Figure 5.14A
Equilibrium
Figure 5.14B

45. Small nonpolar molecules such as O2 and CO2
Diffusion:
Is a result of the kinetic energy of atoms and molecules.  
is driven by entropy.  
requires no input of energy into the system.  
proceeds until equilibrium is reached.
Small nonpolar molecules such as O2 and CO2
Diffuse easily across the phospholipid bilayer of a membrane

46. 5.15 Transport proteins may facilitate diffusion across membranes
Many kinds of molecules
Do not diffuse freely across membranes
For these molecules, transport proteins
Provide passage across membranes through a process called facilitated diffusion
Transport Proteins
Solute molecule
Transport protein
Figure 5.15

47. 5.16 Osmosis is the diffusion of water across a membrane
In osmosis
Water travels from a solution of lower solute concentration to one of higher solute concentration
Equal concentration of solute
Lower concentration of solute
Higher concentration of solute
Solute molecule
H2O
Selectively permeable membrane
Water molecule
Solute molecule with
cluster of water molecules
Figure 5.16
Net flow of water

48. 5.17 Water balance between cells and their surroundings is crucial to organisms
Hypotonic- the concentration of solute outside the cell is lower than the concentration inside the cytosol.
Hypertonic-the concentration of solute outside the cell is higher than the concentration in the cytosol.
A cell that neither gains nor loses water when it is immersed in a solution is isotonic to its environment.
Osmosis
Figure 5.17

49. Osmosis causes cells to shrink in hypertonic solutions
The control of water balance is called osmoregulation.
Osmosis causes cells to shrink in hypertonic solutions
And swell in hypotonic solutions
In isotonic solutions
Animal cells are normal, but plant cells are limp
A plant cell in a hypotonic solution is turgid.

50. Isotonic solution
Hypotonic solution
Hypertonic solution
H2O
H2O
H2O
H2O
Animal cell
(1) Normal
(2) Lysed
(3) Shriveled
Plasma membrane
H2O
H2O
H2O
H2O
Plant cell
(6) Shriveled (plasmolyzed)
(4) Flaccid
(5) Turgid

51. 5.18 Cells expend energy for active transport
Transport proteins can move solutes against a concentration gradient
Through active transport, which requires ATP
Transport protein P P
ATP P
Protein changes shape
Phosphate detaches
Solute
ADP 1
Solute binding 2
Phosphorylation 3
Transport 4
Protein reversion
Figure 5.18

52. Active transport: Uses ATP as an energy source.
Can move solutes up a concentration gradient.
Requires the cell to expend energy.
Is necessary to allow nerves to function properly.

53. 5.19 Exocytosis and endocytosis transport large molecules
To move large molecules or particles through a membrane
A vesicle may fuse with the membrane and expel its contents (exocytosis)
Fluid outside cell
Vesicle
Protein
Cytoplasm
Figure 5.19A

54. Membranes may fold inward
Enclosing material from the outside (endocytosis)
Vesicle forming
Figure 5.19B

55. Endocytosis can occur in three ways Phagocytosis-“cellular eating”
Pinocytosis-“cellular drinking”
Receptor-mediated endocytosis
Plasma membrane
Food being ingested
Pseudopodium of amoeba
Material bound to receptor proteins
PIT
TEM 96,500 
TEM 54,000
Cytoplasm
LM 230
Phagocytosis
Pinocytosis
Receptor-mediated endocytosis
Figure 5.19C

56. http://www. youtube. com/watch

57. 5.20 Faulty membranes can overload the blood with cholesterol
CONNECTION
5.20 Faulty membranes can overload the blood with cholesterol
Harmful levels of cholesterol
Can accumulate in the blood if membranes lack cholesterol receptors
Cells acquire LDLs by receptor-mediated endocytosis.
An inherited lack of functional LDL receptors causes hypercholesterolemia.  
Figure 5.20

58. Phospholipid outer layer
LDL particle
Vesicle
Cholesterol
Protein
Plasma membrane
Receptor protein
Cytoplasm

59. 5.21 Chloroplasts and mitochondria make energy available for cellular work
Enzymes are central to the processes that make energy available to the cell

60. Chloroplasts carry out photosynthesis
Using solar energy to produce glucose and oxygen from carbon dioxide and water
Mitochondria consume oxygen in cellular respiration
Using the energy stored in glucose to make ATP