Chapter 8

1. Chapter 8 An Introduction to Metabolism

2. Concept 8.1: An organism’s metabolism transforms matter and energy, subject to the laws of thermodynamics • __________ is the totality of an organism’s chemical reactions

3. Organization of the Chemistry of Life into Metabolic Pathways • A metabolic pathway begins with a specific molecule and ends with a product • Each step is catalyzed by a specific __________

4. LE 8-UN141 Enzyme 1 Enzyme 2 Enzyme 3 A B D C Reaction 1 Reaction 2 Reaction 3 Starting molecule Product

5. __________ pathways release energy by breaking down complex molecules into simpler compounds • __________ pathways consume energy to build complex molecules from simpler ones

6. Forms of Energy • Energy is the capacity to cause change • Energy exists in various forms, some of which can perform _____

7. __________ energy is energy associated with motion • Heat (thermal energy) is kinetic energy associated with random movement of atoms or molecules • __________ energy is energy that matter possesses because of its location or structure • Chemical energy is potential energy available for release in a chemical reaction • Energy can be __________ from one form to another Animation: Energy Concepts

8. LE 8-2 On the platform, the diver has more potential energy. Diving converts potential energy to kinetic energy. Climbing up converts kinetic energy of muscle movement to potential energy. In the water, the diver has less potential energy.

9. The Laws of Energy Transformation • _______________ is the study of energy transformations • A __________ system, such as that approximated by liquid in a thermos, is isolated from its surroundings • In an __________ system, energy and matter can be transferred between the system and its surroundings • Organisms are _____ systems

10. The First Law of Thermodynamics • According to the first law of thermodynamics, the energy of the universe is __________ • Energy can be transferred and transformed • Energy cannot be created or destroyed • The first law is also called the principle of conservation of energy

11. The Second Law of Thermodynamics • During every energy transfer or transformation, some energy is unusable, often lost as _____ • According to the second law of thermodynamics, every energy transfer or transformation increases the __________ (disorder) of the universe

12. LE 8-3 CO2 Heat Chemical energy H2O First law of thermodynamics Second law of thermodynamics

13. Living cells unavoidably convert organized forms of energy to heat • __________ processes occur without energy input; they can happen _____ or _____ • For a process to occur without energy input, it must increase the entropy of the __________

14. Biological Order and Disorder • Cells create __________ structures from less ordered materials • Organisms also replace ordered forms of matter and energy with less ordered forms • The evolution of more complex organisms does _____ violate the second law of thermodynamics • Entropy (disorder) may decrease in an organism, but the universe’s total entropy __________

15. Free-Energy Change, G • A living system’s free energy is energy that can do _____ when temperature and pressure are uniform, as in a living cell

16. The change in free energy (∆G)during a process is related to the change in enthalpy, or change in total energy (∆H), and change in entropy (T∆S): ∆G = ∆H - T∆S • Only processes with a negative ∆G are __________ • Spontaneous processes can be harnessed to perform work

17. Free Energy, Stability, and Equilibrium • Free energy is a measure of a system’s instability, its tendency to change to a more stable state • During a spontaneous change, free energy decreases and the stability of a system increases • Equilibrium is a state of maximum stability • A process is spontaneous and can perform work only when it is moving toward equilibrium

18. Exergonic and Endergonic Reactions in Metabolism • An __________ reaction proceeds with a net release of free energy and is spontaneous • An __________ reaction absorbs free energy from its surroundings and is nonspontaneous

19. LE 8-6a Reactants Amount of energy released (G < 0) Energy Free energy Products Progress of the reaction Exergonic reaction: energy released

20. LE 8-6b Products Amount of energy required (G > 0) Free energy Energy Reactants Progress of the reaction Endergonic reaction: energy required

21. Equilibrium and Metabolism • Reactions in a closed system eventually reach equilibrium and then do no work • Cells are not in equilibrium; they are open systems experiencing a constant flow of materials • A catabolic pathway in a cell releases free energy in a _____ of reactions • Closed and open hydroelectric systems can serve as analogies

22. LE 8-7a G < 0 G = 0 A closed hydroelectric system

23. LE 8-7b G < 0 An open hydroelectric system

24. LE 8-7c G < 0 G < 0 G < 0 A multistep open hydroelectric system

25. Concept 8.3: ATP powers cellular work by coupling exergonic reactions to endergonic reactions • A cell does three main kinds of work: • Mechanical • Transport • Chemical • To do work, cells manage energy resources by energy __________, the use of an exergonic process to drive an endergonic one

26. The Structure and Hydrolysis of ATP • ATP (adenosine triphosphate) is the cell’s energy shuttle • _____ provides energy for cellular functions

27. LE 8-8 Adenine Phosphate groups Ribose

28. The bonds between the phosphate groups of ATP’s tail can be broken by hydrolysis • Energy is released from ATP when the terminal phosphate bond is broken • This release of energy comes from the chemical change to a state of lower free energy, _____ from the phosphate bonds themselves

29. LE 8-9 P P P Adenosine triphosphate (ATP) H2O + P P P + Energy i Adenosine diphosphate (ADP) Inorganic phosphate

30. In the cell, the energy from the exergonic reaction of ATP hydrolysis can be used to drive an endergonic reaction • Overall, the coupled reactions are exergonic

31. LE 8-10 Endergonic reaction: DG is positive, reaction is not spontaneous NH2 NH3 DG = +3.4 kcal/mol + Glu Glu Ammonia Glutamine Glutamic acid Exergonic reaction: DG is negative, reaction is spontaneous P ATP ADP DG = –7.3 kcal/mol H2O + + i Coupled reactions: Overall DG is negative; together, reactions are spontaneous DG = –3.9 kcal/mol

32. How ATP Performs Work • ATP drives endergonic reactions by __________, transferring a __________ group to some other molecule, such as a reactant • The recipient molecule is now __________ • The three types of cellular work (mechanical, transport, and chemical) are powered by the hydrolysis of ATP

33. LE 8-11 P i P Protein moved Motor protein Mechanical work: ATP phosphorylates motor proteins Membrane protein ADP ATP + P i P P i Solute transported Solute Transport work: ATP phosphorylates transport proteins P NH2 NH3 P + + Glu i Glu Reactants: Glutamic acid and ammonia Product (glutamine) made Chemical work: ATP phosphorylates key reactants

34. The Regeneration of ATP • ATP is a renewable resource that is __________ by addition of a phosphate group to _____ • The energy to phosphorylate ADP comes from __________ reactions in the cell • The chemical __________ energy temporarily stored in ATP drives most cellular work

35. LE 8-12 ATP Energy for cellular work (endergonic, energy- consuming processes) Energy from catabolism (energonic, energy- yielding processes) P ADP + i

36. Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers • A __________ is a chemical agent that speeds up a reaction without being ________ by the reaction • An enzyme is a catalytic __________ • Hydrolysis of sucrose by the enzyme sucrase is an example of an enzyme-catalyzed reaction

37. LE 8-13 Sucrose C12H22O11 Glucose C6H12O6 Fructose C6H12O6

38. The Activation Energy Barrier • Every chemical reaction between molecules involves bond __________ and bond __________ • The initial energy needed to start a chemical reaction is called the free energy of activation, or __________ energy (EA) • Activation energy is often supplied in the form of heat from the surroundings

39. LE 8-14 B A C D Transition state EA B A Free energy D C Reactants B A DG < O C D Products Progress of the reaction

40. How Enzymes Lower the EA Barrier • Enzymes catalyze reactions by lowering the _____ barrier • Enzymes do not affect the change in __________ (∆G); instead, they ________ reactions that would occur eventually Animation: How Enzymes Work

41. LE 8-15 Course of reaction without enzyme EA without enzyme EA with enzyme is lower Reactants Free energy Course of reaction with enzyme DG is unaffected by enzyme Products Progress of the reaction

42. Substrate Specificity of Enzymes • The reactant that an enzyme acts on is called the enzyme’s __________ • The enzyme binds to its substrate, forming an __________ complex • The __________ is the region on the enzyme where the substrate binds • __________ of a substrate brings chemical groups of the active site into positions that enhance their ability to catalyze the reaction

43. LE 8-16 Substrate Active site Enzyme-substrate complex Enzyme

44. Catalysis in the Enzyme’s Active Site • In an enzymatic reaction, the substrate binds to the active site • The active site can lower an EA barrier by • Orienting substrates correctly • Straining substrate bonds • Providing a favorable microenvironment • Covalently bonding to the substrate

45. LE 8-17 Substrates enter active site; enzyme changes shape so its active site embraces the substrates (induced fit). Substrates held in active site by weak interactions, such as hydrogen bonds and ionic bonds. • Active site (and R groups of • its amino acids) can lower EA • and speed up a reaction by • acting as a template for • substrate orientation, • stressing the substrates • and stabilizing the • transition state, • providing a favorable • microenvironment, • participating directly in the • catalytic reaction. Substrates Enzyme-substrate complex Active site is available for two new substrate molecules. Enzyme Products are released. Substrates are converted into products. Products

46. Effects of Local Conditions on Enzyme Activity • An enzyme’s activity can be affected by: • General environmental factors, such as __________ and _____ • Chemicals that specifically influence the enzyme

47. Effects of Temperature and pH • Each enzyme has an optimal temperature in which it can function • Each enzyme has an optimal pH in which it can function

48. LE 8-18 Optimal temperature for typical human enzyme Optimal temperature for enzyme of thermophilic (heat-tolerant bacteria) Rate of reaction 40 0 20 60 80 100 Temperature (°C) Optimal temperature for two enzymes Optimal pH for pepsin (stomach enzyme) Optimal pH for trypsin (intestinal enzyme) Rate of reaction 2 3 6 7 9 10 0 1 4 5 8 pH Optimal pH for two enzymes

49. Cofactors • __________ are nonprotein enzyme helpers • __________ are organic cofactors

50. Enzyme Inhibitors • __________ inhibitors bind to the active site of an enzyme, competing with the substrate • __________ inhibitors bind to another part of an enzyme, causing the enzyme to change shape and making the active site less effective