Bioenergetics

1. Bioenergetics Intro/Chpt 14

2. Catabolism & energy prod’n in cells (Fig. 4, p487) • Glycolysis • Intermediary metabolism • ATP production • Mitochondrial • Chloroplast

3. Fig. 4, p.487

4. Regulatory enzymes • Rate limiting • Modulators control +/- • Allosteric • Covalently modified • Combination • Pathway commitment

5. Metabolic rxns follow trends • ~ 50 rxns • Only 5 major types (REMEMBER?) • Coupling • Redox rxns impt

6. Thermodynamics (again!) • D G = D H - T D S • D G - = Exergonic = heat given off • D H - = Energy released w/ bonding rxn • D S + = Increased entropy (incr’d randomness) • D Go’ = Std free energy (pH=7, [H2O]=55 M, [reactant]=1 M, T=25oC) = physio cond’s in cell

7. Thermodynamics (again!) • For cellular rxn: a A + b B <= > c C + d D at equilib • K’eq can be written • K’eq related to D Go’ (Table 14-2) • Can predict D Go’ from Keq and vice/versa (Table 14-3)

10. In real life • Not all reactants @ 1 M • Go back to D G • D G = D Go’ + RT ln ([C]c[D]d/[A]a[B]b) • Theoretical max energy for rxn • Actual energy available to system < theoretical

11. In real life – cont’d • Not all thermodynamically favorable rxns proceed at measurable speeds • Enzyme catalysis impt • D G relationship to k is inverse and exponential (REMEMBER??) • D G stays the same

12. In sequential reactions • If common reactants, products: • D Go’ values are additive • So thermo’ly unfavorable rxn can be driven by thermo’ly favorable rxn coupled to it • Keq values are multiplied • So see large differences in Keq of coupled rxns • Commonly coupled to endergonic rxns: • ATP hydrolysis: D Go’ = -30.5 kJ/mole • Coupling hydrol of n ATPs raises Keq by 108n

13. ATP hydrolysis adds energy • Products of hydrolysis are resonance stabilized (14-1) • Decr’d electrostatic repulsions in ADP • Pi O’s can share – charge

14. Fig. 14-1

15. ATP hydrolysis adds energy • Mg coordinates w/ ADP (14-2)

16. ATP hydrolysis adds energy • Pi or AMP often cov’ly couples w/ reactants •  High energy intermediate • Larger D G when cleaved • Glutamate (14-8) • First step in glycolysis activates glucose

17. Fig. 14-8

18. Some notes… • ATP may bind non-covalently to protein; hydrolysis provides energy for conform’l change • Ex: Na+/K+ ATPase • Other phosphorylated cmpds release energy w/ cleavage of Pi (Table 14-6) • Products also often resonance stabilized (14-3, 14-4) • BUT original source of Pi is ATP  ADP + Pi

20. Fig. 14-3

21. Fig. 14-4

22. Some (more) notes… • Thioesters impt • Acetyl CoA example (14-6) • Greater D G for hydrolysis (14-7) • Nucleoside triphosphates are source of nucleotides inc’d into DNA, RNA (w/ release of energy) (14-12)

23. Fig. 14-6

24. Fig. 14-7

25. Fig. 14-12

26. Biological Oxidation Reduction Reactions (Redox) • Flow of e-’s changes redox state of reactants, products • Reactant that goes from more red’d  more ox’d • e-’s accepted by another molecule, goes from more ox’d  more red’d

27. Redox Rxns – cont’d • Battery as example of e- flow  energy • Two linked sol’ns w/ differences in affinities for e- • Coupled through e- carrier • Carrier associated w/ motor, which can give off energy (in the form of work)

28. Redox Rxns – cont’d • Cellular analogy • Two sol’ns = two molecules w/ differing affinities for e- • e- carrier = cofactor (molecule) • Motor = ATP synthesis “machine” in mitochondrion which can give off energy (in the form of a chemical with high potential chemical energy)

29. Redox Rxns – cont’d • Metabolism of nutrients converts cmpds from more red’d  more ox’d states • By LEO/GER, nutrient loses electrons (e-‘s) • e-‘s released to system BUT are NOT free in cytoplasm • e-‘s transferred to carrier mol’s • By LEO/GER, carrier mol’s now red’d

30. Biological Oxidation Reduction Reactions (Redox) – cont’d • Red’d carrier mol’s bring e-‘s to mitoch • Electron transport system • Coupled to oxidative phosph’n •  ATP prod’d

31. Redox Rxn’s (cont’d) • Rxns of e- flow (reductant [or e- donor]  oxidant [or e- acceptor]) can be additive • Imptc – free energy of system changes w/ change in red’n potential of reactants/products in rxn • D E = diff in red’n potentials of reductant, oxidant • Related to free energy of system ( D G) (eq’n 14-6) • Use to calc D G’s for biol. oxn’s

32. Redox Rxn’s (cont’d) • e- flow from lower red’n potential  higher red’n potential (Table 14-7) • Eo’ additive if coupled rxns have common intermed’s • Use to calc D G’s for biol. oxn’s

33. Redox Rxn’s (cont’d) • Cells’ rxns (incl redox) involve organic cmpds • Consider “ownership” of e- by C in a cmpd (14-13) • Ox’n C-cont’ng cmpds often w/ bonding O to C, displacing H • More red’d cmpds – more H’s, fewer O’s • More ox’d compds – more O’s, fewer H’s

34. Fig. 14-13

35. Redox Rxn’s (cont’d) • Oxidation may occur in 4 ways • Electrons transfer directly • As H+ + e- • As combination w/ O2 • As :H- (hydride ion) • Common mechanism w/ carriers • “Reducing equivalents”

36. Nicotinamides -- NAD, NADP • When ox’d: NAD+, when red’d: NADH • One C on nicotinamide ring accepts e- as :H- • Hydride donor also releases one H+ to system • Overall: NAD+ + 2e- + 2H+  NADH + H+

37. Fig. 14-15a

38. NAD, NADP – cont’d • NADP+ preferred by some enz’s, species • [NAD+/NADH] >> [NADP+/NADPH] • [NAD+] usually > [NADH] • Commonly donates or accepts hydride? • [NADP+] usually < [NADPH] • Enz’s = oxidoreductases or dehdrogenases • > 200 (Table 14-8) • Loosely assoc’d w/ deHases • Move between enzymes • Recycled by cell

40. Flavin Nucleotides – FMN, FAD • Der’d from riboflavin • Isoalloxazine ring accepts 1 or 2 e- • Semiquinone (partly red’d) • Quinone (fully red’d) • Often bound more tightly to enz’s • “Prosthetic grps” • Varied enz’s associate w/ flavins • Table 14-9

41. Fig. 14-16