CHAPTER 6 Energy, Enzymes, and Metabolism

1. CHAPTER 6Energy, Enzymes, and Metabolism

2. Chapter 6: Energy, Enzymes, and Metabolism Energy and Energy Conversions ATP: Transferring Energy in Cells Enzymes: Biological Catalysts

3. Chapter 6: Energy, Enzymes, and Metabolism Molecular Structure Determines Enzyme Function Metabolism and the Regulation of Enzymes

4. Energy and Energy Conversions • Energy is the capacity to do work. • Potential energy is the energy of state or position; it includes energy stored in chemical bonds. • Kinetic energy is the energy of motion. 4

5. Energy and Energy Conversions • Potential energy can be converted to kinetic energy, which does work. Review Figure 6.1 5

6. figure 06-01.jpg 6.1 Figure 6.1

7. Energy and Energy Conversions • The first law of thermodynamics tells us energy cannot be created or destroyed. • The second tells us that, in a closed system, the quantity of energy available to do work decreases and unusable energy increases. Review Figure 6.3 7

8. figure 06-03.jpg 6.3 Figure 6.3

9. Energy and Energy Conversions • Living things obey the laws of thermodynamics. • Organisms are open systems that are part of a larger closed system. Review Figure 6.4 9

10. figure 06-04.jpg 6.4 Figure 6.4

11. Energy and Energy Conversions • Changes in free energy, total energy, temperature, and entropy are related by the equation DG =DH – TDS. 11

12. Energy and Energy Conversions • Spontaneous, exergonic reactions release free energy and have a negativeDG. • Non-spontaneous, endergonic reactions take up free energy, have a positiveDG, and proceed only if free energy is provided. Review Figure 6.5 12

13. figure 06-05.jpg 6.5 Figure 6.5

14. Energy and Energy Conversions • The change in free energy of a reaction determines its point of chemical equilibrium, at which forward and reverse reactions proceed at the same rate. • For spontaneous, exergonic reactions, the equilibrium point lies toward completion. Review Figure 6.6 14

15. figure 06-06.jpg 6.6 Figure 6.6

16. ATP: Transferring Energy in Cells • ATP serves as an energy currency in cells. • Hydrolysis of ATP releases a relatively large amount of free energy. Review Figure 6.8 16

17. figure 06-08.jpg 6.8 Figure 6.8

18. ATP: Transferring Energy in Cells • The ATP cycle couples exergonic and endergonic reactions, transferring free energy from the exergonic to the endergonic reaction. Review Figures 6.9, 6.10 18

19. figure 06-09.jpg 6.9 Figure 6.9

20. figure 06-10.jpg 6.10 Figure 6.10

21. Enzymes: Biological Catalysts • The rate of a chemical reaction is independent ofDGbut is determined by the size of the activation energy barrier. • Catalysts speed reactions by lowering the barrier. Review Figures 6.11, 6.12 21

22. figure 06-11.jpg 6.11 Figure 6.11

23. figure 06-12.jpg 6.12 Figure 6.12

24. Enzymes: Biological Catalysts • Enzymes are biological catalysts, highly specific for their substrates. • Substrates bind to the active site, where catalysis takes place, forming an enzyme–substrate complex. Review Figure 6.13 24

25. figure 06-13.jpg 6.13 Figure 6.13

26. Enzymes: Biological Catalysts • At the active site, a substrate can be oriented correctly, chemically modified, or strained. • As a result, the substrate readily forms its transition state, and the reaction proceeds. Review Figures 6.14, 6.15 26

27. figure 06-14.jpg 6.14 Figure 6.14

28. figure 06-15.jpg 6.15 Figure 6.15

29. Enzymes: Biological Catalysts • Substrate concentration affects the rate of an enzyme-catalyzed reaction. Review Figure 6.16 29

30. figure 06-16.jpg 6.16 Figure 6.16

31. Molecular Structure Determines Enzyme Function • The active site where substrate binds determines the specificity of an enzyme. • Upon binding to substrate, some enzymes change shape, facilitating catalysis. Review Figures 6.13, 6.18 31

32. figure 06-18.jpg 6.18 Figure 6.18

33. Molecular Structure Determines Enzyme Function • Some enzymes require cofactors for catalysis. • Prosthetic groups are permanently bound to the enzyme. • Coenzymes usually are not. • They enter into the reaction as a “cosubstrate,” as they are changed by the reaction and released from the enzyme. Review Table 6.1 33

34. table 06-01.jpg Table 6.1 Table 6.1

35. Metabolism and the Regulation of Enzymes • Metabolism is organized into pathways: the product of one reaction is a reactant for the next. • Each reaction is catalyzed by an enzyme. 35

36. Metabolism and the Regulation of Enzymes • Enzyme activity is subject to regulation. • Some compounds react irreversibly with them and reduce their catalytic activity. • Others react reversibly, inhibiting enzyme action temporarily. • A compound structurally similar to an enzyme’s normal substrate may inhibit enzyme action. Review Figures 6.20, 6.21 36

37. figure 06-20.jpg 6.20 Figure 6.20

38. figure 06-21a.jpg 6.21 – Part 1 Figure 6.21 – Part 1

39. figure 06-21b.jpg 6.21 – Part 2 Figure 6.21 – Part 2

40. Metabolism and the Regulation of Enzymes • For allosteric enzymes, plots of reaction rate versus substrate concentration are sigmoidal, in contrast to plots of the same variables for non-allosteric enzymes. Review Figure 6.22 40

41. figure 06-22.jpg 6.22 Figure 6.22

42. Metabolism and the Regulation of Enzymes • Allosteric inhibitors bind to a site different from the active site and stabilize the inactive form of the enzyme. • The multiple catalytic subunits of many allosteric enzymes interact cooperatively. Review Figure 6.23 42

43. figure 06-23.jpg 6.23 Figure 6.23

44. Metabolism and the Regulation of Enzymes • The end product of a metabolic pathway may inhibit the allosteric enzyme that catalyzes the commitment step of the pathway. Review Figure 6.24 44

45. figure 06-24.jpg 6.24 Figure 6.24

46. Metabolism and the Regulation of Enzymes • Enzymes are sensitive to their environment. • Both pH and temperature affect enzyme activity. Review Figures 6.25, 6.26 46

47. figure 06-25.jpg 6.25 Figure 6.25

48. figure 06-26.jpg 6.26 Figure 6.26