1. CHAPTER 5
The Working Cell

6. Biology and Society: Stonewashing Without the Stones
The sturdy cotton fabric denim has been worn because of its toughness and appeal.
Stonewashing jeans with pumice stone can damage the fabric.
Recently the enzyme cellulase has been used to achieve better results.
Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

7. Figure 5.1

8. Some Basic Energy Concepts
Energy makes the world go around.
What is energy?

9. Conservation of Energy
Energy is defined as the capacity to perform work.
Kinetic energy is the energy of motion.
Potential energy is stored energy.
Energy Concepts

10. Figure 5.2

11. Energy can be changed from one form to another.
However, it cannot be created or destroyed.
This is the conservation of energy principle.

12. Entropy Heat Is a type of kinetic energy.
Is a product of all energy conversions.

13. Scientists use the term entropy as a measure of disorder, or randomness.
All energy conversions increase the entropy of the universe.

14. Chemical Energy Chemical energy Is a form of potential energy.
Is found in food, gasoline, and other fuels.

15. Living cells and automobile engines use the same basic process to make chemical energy do work.

16. Figure 5.3a

17. Figure 5.3b

18. Cellular respiration
Is the energy-releasing chemical breakdown of fuel molecules.
Provides energy for the cell to do work.

19. Food Calories
A calorie is the amount of energy that raises the temperature of one gram of water by one degree Celsius.

20. The kilocalorie is 1,000 calories.
The unit used to measure the energy in food.

21. Figure 5.4a

22. The energy of calories in food is burned off by many activities.

23. Figure 5.4b

24. ATP and Cellular Work
The chemical energy of organic molecules is released in cellular respiration to make ATP in the mitochondria.

25. ATP (adenosine triphosphate)
The Structure of ATP
ATP (adenosine triphosphate)
Consists of adenosine plus a tail of three phosphate groups.
Is broken down to ADP, accompanied by the release of energy.

26. Figure 5.5

27. ATP can energize other molecules by transferring phosphate groups.
Phosphate Transfer
ATP can energize other molecules by transferring phosphate groups.
This energy can be used to drive cellular work.

28. Figure 5.6

29. The ATP Cycle
Cellular work spends ATP.
ATP is recycled from ADP and phosphate through cellular respiration.

30. ATP functions in what is called energy coupling, or the ATP cycle.

31. Figure 5.7

32. Enzymes
Metabolism is the sum total of all chemical reactions that occur in organisms.
Few metabolic reactions occur without the assistance of enzymes.

33. Activation Energy Activation energy Enzymes
Is the energy that activates the reactants in a chemical reaction.
Triggers a chemical reaction to proceed.
Enzymes
Lower the activation energy for chemical reactions.

34. Figure 5.8

35. Each enzyme is very selective.
Induced Fit
Each enzyme is very selective.
It catalyzes specific reactions.

36. Each enzyme recognizes a specific substrate.
The active site fits to the substrate, and the enzyme changes shape slightly.
This interaction is called induced fit.

37. Enzymes can function over and over again.
This is a key characteristic of enzymes.
How Enzymes Work

38. Figure 5.9

39. Enzyme Inhibitors Enzyme inhibitors Can inhibit a metabolic reaction.
Bind to the active site, as substrate imposters.

40. Figure 5.10a, b

41. Other inhibitors Bind at a remote site, changing the enzyme’s shape.
In some cases, this is called feedback regulation.

42. Figure 5.10c

43. Membrane proteins perform a variety of functions.
Membrane Function
Working cells must control the flow of materials to and from the environment.
Membrane proteins help with this task.
Membrane proteins perform a variety of functions.
Membrane Selectivity

44. Figure 5.11

45. Passive Transport: Diffusion Across Membranes
Molecules contain heat energy.
They vibrate and wander randomly.

46. Diffusion is one result of the movement of molecules.
Molecules tend to spread into the available space.
Diffusion is passive transport; no energy is needed.
Diffusion

47. Figure 5.12

48. Another type of passive transport is facilitated diffusion, the transport of some substances by specific transport proteins that act as selective corridors.

49. Osmosis and Water Balance in Cells
Osmosis is the passive transport of water across a selectively permeable membrane.
Osmosis

50. Figure 5.13

51. A hypertonic solution A hypotonic solution An isotonic solution
Has a higher concentration of solute.
A hypotonic solution
Has a lower concentration of solute.
An isotonic solution
Has an equal concentration of solute.

52. Water Balance in Animal Cells
The survival of a cell depends on its ability to balance water uptake and loss.
Plasmolysis
Turgid Elodea

53. Figure 5.14

54. Osmoregulation is the control of water balance in animals.

55. Water Balance in Plant Cells
Water balance in plant cells is different.
They have rigid cell walls.
They are at the mercy of the environment.

56. Figure 5.15

57. Active Transport: The Pumping of Molecules Across Membranes
Active transport requires energy to move molecules across a membrane.
Active Transport
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58. Figure 5.16

59. Exocytosis and Endocytosis: Traffic of Large Molecules
Secretes substances outside of the cell.
Exocytosis and Endocytosis Introduction
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60. Figure 5.17a

61. Endocytosis
Takes material into the cell.
Pinocytosis

62. Figure 5.17b

63. In phagocytosis (“cellular eating”), a cell engulfs a particle and packages it within a food vacuole.
In pinocytosis (“cellular drinking”), a cell “gulps” droplets of fluid by forming tiny vesicles.
Phagocytosis

64. Figure 5.18

65. Receptor-mediated endocytosis
Is triggered by the binding of external molecules to membrane proteins.
Receptor-Mediated Endocytosis

66. Figure 5.19

67. The Role of Membranes in Cell Signaling
Cellular communication
Begins with the reception of an extracellular signal.
The signal transduction pathway
Consists of proteins and other molecules that relay the signal.

68. Figure 5.20

69. Evolution Connection: Evolving Enzymes
Organisms use many different enzymes.
How could such diversity arise?
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70. Analysis of genetic sequences suggests that
Distinct enzymes came about through molecular evolution.

71. A lab procedure called directed evolution, in which genes for a particular enzyme were mutated at random,
Produced new enzymes that recognized new substrates.

72. Figure 5.21