1. Ground Rules of Metabolism Chapter 6

2. 6.1 What Is Energy? Capacity to do work Forms of energy –Potential energy –Kinetic energy –Chemical energy

3. What Can Cells Do with Energy? Energy inputs become coupled to energy-requiring processes Cells use energy for: –Chemical work –Mechanical work –Electrochemical work

4. First Law of Thermodynamics The total amount of energy in the universe remains constant Energy can undergo conversions from one form to another, but it cannot be created or destroyed

5. One-Way Flow of Energy The sun is life’s primary energy source Producers trap energy from the sun and convert it into chemical bond energy All organisms use the energy stored in the bonds of organic compounds to do work

6. Second Law of Thermodynamics No energy conversion is ever 100 percent efficient The total amount of energy is flowing from high-energy forms to forms lower in energy

7. Entropy Measure of degree of disorder in a system The world of life can resist the flow toward maximum entropy only because it is resupplied with energy from the sun

8. 6.2 Energy Changes & Cellular Work Energy changes in cells tend to run spontaneously in the direction that results in a decrease in usable energy

9. Endergonic Reaction + 60 2 and 6H 2 O Energy in energy-poor starting substances 612 glucose - a product with more energy Figure 6.5a,b Page 100

10. Exergonic Reaction Energy out glucose - energy-rich starting substance + 60 2 products with less energy 66 Figure 6.5a,b Page 100

11. Structure of ATP three phosphate groups sugar (ribose) nucleotide base (adenine) Figure 6.6b Page 101

12. ATP: Main Energy Carrier ATP couples energy inputs and outputs ATP/ADP cycle regenerates ATP energy input ADP + P i ATP energy output

13. Electron Transfers Oxidation - lose electron Reduction - gain electron Central to the formation of ATP during photosynthesis and aerobic respiration

14. 6.3 Participants in Metabolic Pathways Energy Carriers Enzymes Cofactors Reactants Intermediates Products

15. Degradative and Anabolic Pathways ATP BIOSYNTHETIC PATHWAYS (ANABOLIC) ENERGY INPUT DEGRADATIVE PATHWAYS (CATABOLIC) energy-poor products large energy-rich molecules simple organic compounds ADP + P i

16. Types of Reaction Sequences BRANCHING PATHWAY LINEAR PATHWAY CYCLIC PATHWAY ABCDE F KJI G NML H Figure 6.8 Page 102

17. Which Way Will a Reaction Run? Nearly all chemical reactions are reversible Direction reaction runs depends upon –Energy content of participants –Reactant-to-product ratio

18. Chemical Equilibrium HIGHLY SPONTANEOUS EQUILIBRIUM HIGHLY SPONTANEOUS RELATIVE CONCENTRATION OF PRODUCT RELATIVE CONCENTRATION OF REACTANT Figure 6.9 Page 103

19. Chemical Equilibrium Energy in the reactants equals that in the products Product and reactant molecules usually differ in energy content Therefore, at equilibrium, the amount of reactant almost never equals the amount of product

20. No Vanishing Atoms Law of conservation of mass Reactions rearrange atoms, but they never destroy them As many atoms of each element in all the products as there were in all the reactants

21. 6.4 Electron Transfer Chains Arrangement of enzymes, coenzymes, at cell membrane As one molecule is oxidized, next is reduced Create H + concentration and electric gradients that are used for making ATP

22. 6.5 Enzyme Structure and Function Enzymes are catalytic molecules They speed the rate at which reactions approach equilibrium

23. Four Features of Enzymes 1) Enzymes do not make anything happen that could not happen on its own. They just make it happen much faster. 2) Reactions do not alter or use up enzyme molecules.

24. Four Features of Enzymes 3) The same enzyme usually works for both the forward and reverse reactions. 4) Each type of enzyme recognizes and binds to only certain substrates.

25. Activation Energy For a reaction to occur, an energy barrier must be surmounted Enzymes make the energy barrier smaller activation energy without enzyme activation energy with enzyme energy released by the reaction products starting substance Figure 6.12a Page 105

26. Activation Energy Used to: Align reactive chemical groups Briefly destabilize electric charges Rearrange, create, and break bonds

27. 6.6 Transition State Point when a reaction can easily run in either direction, to product or back to a reactant Substrate is bound most tightly to an enzyme in this state

28. Mechanisms of Bringing about Transition State Helping substrates get together Orienting substrates in positions favoring reaction Shutting out water Inducing changes in enzyme shape

29. Factors Influencing Enzyme Activity Coenzymes and cofactors Allosteric regulators Temperature pH Salt concentration

30. 6.7 How Is Enzyme Activity Controlled? Allosteric Activation Allosteric Inhibition Feedback Inhibition

31. Allosteric Activation allosteric activator vacant allosteric binding site active site altered, can bind substrate active site cannot bind substrate enzyme active site Figure 6.15a Page 108

32. Allosteric Inhibition allosteric inhibitor allosteric binding site vacant; active site can bind substrate active site altered, can’t bind substrate Figure 6.15b Page 108

33. Feedback Inhibition enzyme 2enzyme 3enzyme 4enzyme 5 enzyme 1 SUBSTRATE END PRODUCT (tryptophan) A cellular change, caused by a specific activity, shuts down the activity that brought it about Figure 6.16 Page 108

34. Effect of Temperature Small increase in temperature increases molecular collisions, reaction rates High temperatures disrupt bonds and destroy the shape of active site Figure 6.17b Page 109

35. Effect of pH Figure 6.17c Page 109