Cellular Respiration: Harvesting Chemical Energy

1. Figure 9.1 Lecture 13 9/30/05 Cellular Respiration: Harvesting Chemical Energy Chapter 9 • General • Principles

2. Lecture Outline • Regulation of Enzymes: competitive, allosteric, phosphorylation • 2. Equilibrium • 3. Digestion vs Metabolism: catabolism and anabolism • 4. What is a metabolic pathway? • 5. Feedback regulation of pathways • 6. Catabolic pathways - stepping down the oxidation series of carbon • 7. Harvesting energy from redox reactions • - substrate level phosphorylation ATP • – reducing equivalent carriers NADH + H+, FADH2 • 8. Example of a catabolic pathway: Fatty Acid Oxidation

3. Cannot Do work Can do Useful work ∆G < 0 ∆G = 0 (a) A closed hydroelectric system. Water flowing downhill turns a turbine that drives a generator providing electricity to a light bulb, but only until the system reaches equilibrium. Figure 8.7 A Reactions that proceed in a closed system • Eventually reach equilibrium

4. ∆G < 0 (b) An open hydroelectric system. Flowing water keeps driving the generator because intake and outflow of water keep the system from reaching equlibrium. Figure 8.7 Living systems = Open System • Must have constant flow of materials in • Constant Energy Input Equilibrium to a living system is called….

5. Metabolism – totality of all chemical reactions of an organism digestion Hydrolysis of polymers to monomers No energy Harvested ! occurs “outside” the cell catabolism– energy capture reactions oxidize substrates, produce energy carriers anabolism– energy utilizing reactions use energy carriers, build things Note: DG<0

6. ∆G < 0 ∆G < 0 ∆G < 0 Metabolism: a series of favorable reactions Inputs Figure 8.7 Waste Products Metabolic Pathway: The product of each reaction becomes the reactant for a next, so no reaction reaches equilibrium

7. Metabolic Pathway Enzymes work in series Each enzyme carries out one reaction Reactions in series constitute a Pathway Enzyme 1 promotes reaction AB Enzyme 2 promotes reaction BC Enzyme 3 promotes reaction CD Enzyme 4 promotes reaction DE Enzyme 5 promotes reaction EF Enzyme 6promotes reaction FG So as long as have A, G will be produced Each reaction is facilitated by a different enzyme

8. A F F A Enzyme 1 Enzyme 2 Enzyme 3 B E A D C B A A F F Reaction 1 Reaction 2 Reaction 3 Product Startingmolecule C D Chemistry of Life is organized into Metabolic Pathways

9. FeedbackRegulation F A F F A B E A A F F C D “Plenty of F over Here, Shut it OFF!” Enzymes can be regulated Allosteric modulator ?

10. thr Initial substrate(threonine) Active siteavailable Threoninein active site Enzyme 1(threoninedeaminase) Isoleucineused up bycell Intermediate A Feedbackinhibition Enzyme 2 Active site of enzyme 1 no longer binds threonine;pathway is switched off Intermediate B Enzyme 3 Intermediate C Isoleucine binds to allosteric site Enzyme 4 Intermediate D Enzyme 5 Figure 8.21 End product(isoleucine) Product Of Pathway Is Allosteric Regulator Of First Enzyme In Pathway ile

11. For example, oxidation of glucose: C6H12O6 (glucose) + 6O2 6CO2 + 6H2O DG= -686 kcal/molDH = -673 kcal/mol TDS= -13 kcal/mol in the cell, this is done in >21 steps! Capture the energy in small packets ie, 36 ATP units of 7.3 kcal Why so many steps in a pathway?

12. 15 gallons Of gasoline Many Small Controlled reactions

13. catabolic pathway Oxidize in discrete steps Step down the oxidation series of carbon some activation step oxidation step, with energy harvest reorganization step oxidation step, another harvest etc yield product of pathway

14. Organic Reductions X + 2e- + 2H+ XH2 Organic Oxidation YH2 Y + 2e- +2H+ What is an OXIDATION? • For ionic species: • Reduced means • “rich” in electrons • Oxidized means • “fewer” electrons • Fe++reduced Fe+++oxidized Oxidation: loss of e- Reduction : gain of e-

15. Reduced = High enthalpy • “few” bonds to oxygen • “many” bonds to hydrogen Ease of Removing electrons electronegativity Oxidized “few” bonds to oxygen “many” bonds to hydrogen

16. OXIDATION series of carbon Highly reduced Hydrocarbon chain Unsaturated hydrocarbon Alcohol Carbonyl Carboxylic Acid Carbon Dioxide R-CH=CH2 Highly oxidized

17. In Metabolism: • Highly reducedfully oxidized • CH3-CH2-CH2-(CH2)x-CH2-C-O + O2 H2O + CO2 + energy • Fatty acid O (captured) • Partially reduced fully oxidized • + O2 H2O + CO2+ energy • carbohydrate (captured)

18. “H-H” removed “H- + H+” removed R-CH2-C=O H “2e- + H+ + H+” removed” R-CH2-C=O OH Catabolic Pathways Progress down the Oxidation Series Of Carbon R-CH2 -CH 3 R-CH=CH2 R-CH2-CH2 -OH “adding O” O=C=O

19. Products Reactants becomes oxidized + + + Energy 2O2 CO2 2 H2O CH4 becomes reduced H C O O C O O O H H H H H Carbon dioxide Water Oxygen(oxidizingagent) Methane(reducingagent) REDOX Reactions Oxidations always paired with reductions If one thing gets oxidized, another becomes reduced Change the degree of electron sharing in covalent bonds Figure 9.3

20. Carriers of Reducing Equivalents CoEnzymes (CoFactors) NAD+ nicotinamide adenine dinucleotide NAD+ + H+ + 2e- -> NADH NADP+ nicotinamide adenine dinucleotide phosphate NADP+ + H+ + 2e- -> NADPH FAD flavin adenine dinucleotide FAD+ 2H+ + 2e- -> FADH2

21. 2 e– + 2 H+ 2 e– + H+ NAD+ NADH H O O H H Reduction of NAD+ + + 2[H] C NH2 NH2 C H+ (from food) Oxidation of NADH N N+ Nicotinamide(reduced form) Nicotinamide(oxidized form) CH2 O O O O– P O H H OH O HO O– P NH2 HO CH2 O N N H N H N O H H HO OH Figure 9.4 Electrons from organic compounds Are usually first transferred to NAD+, a coenzyme

22. e- 1 e- 1 H+ 2 e- 2 H+ NAD+ to NADH Carries 2e- and 1 H+

23. NADP+ looks like this: H+ NADP+ NADPH H+ 2e-

24. FAD looks like this: 1 e- 1 H+ 1 e- 1 H+ FAD to FADH2 Carries 2e- and 2 H+

25. How harvest energy packets upon oxidation? - high energy phosphate bonds ATP, GTP production substrate level phosphorylation less usual form of energy harvest • Carriers of reducing equivalents • Oxidized form – reduced form • NAD+ NADH + H+ • FAD FADH2 • Can cash in reduced carriers for ATP • oxidative phosphorylation

26. Carriers of Energy potential ATP – common energy currency“$$$” High energy phosphate bonds

27. Substrate Level Phosphorylation “B” (ATP) O = ADP-Pi “C” Enzyme 2 R- C-Pi + ADP-OH O = R- C-OH Energy of Oxidations “Captured” in the FORMATION of ATP Oxidized to ACID Example: NAD+ NADH + H+ “B” “A” OO OO Enzyme 1 = = = = R- C -C-OH R- C-PiC Pi = High Energy Compound O Oxidized to Carbon Dioxide

28. Poker chips • Can cash in reduced carriers for ATP • oxidative phosphorylation How harvest energy packets upon oxidation? - high energy phosphate bonds ATP, GTP production substrate level phosphorylation less usual form of energy harvest $$$ • Carriers of reducing equivalents • Oxidized form – reduced form • NAD+ NADH + H+ • FAD FADH2

29. 2e- 2H+ Captured in catabolism 2e- 2H+ Cashed in The Regeneration Energy Carriers Energy carriers (ATP, NAD+, FAD) present in only minute amounts NADH + H+ Energy from catabolism (exergonic, energy yielding processes) Energy for cellular work (endergonic, energy- consuming processes) NAD+

30. Let’s put it together Step down oxidation series Harvest energy in discrete packets Fatty Acid Oxidation Pathway

31. CH3-CH2-R-CH2-CH2-C=O ATP + CoA-SH Fatty acid O- CH3-CH2-R-CH2-CH2-C=O ADP + Pi Fatty acyl CoA S-CoA Start of Pathway Priming Step (energy input)

32. Fatty Acid Oxidation (b-oxidation) Priming Step Saturated hydrocarbon 2e- 2 H+ removed -steps down oxidation states of carbon Ester (acid) unsaturated hydrocarbon -captures Reducing potential NADH + H+ FADH2 Ketone 2e- 2 H+ removed alcohol

33. Oxidation of Carbon -CH2- to –C=O to acid S CoA Net Result of Fatty Acid Oxidation Pathway Fatty acid shortened by 2 carbon unit 2 carbon acid attached to CoA (acetyl CoA) Capture reducing equivalents 2 NADH + H+ 2 FADH2

34. Summary • Digestion, Metabolism, Catabolism, Anabolism • Biochemical Pathway; feedback regulation • Catabolic Pathways • - Step down oxidation series of carbon • - Harvest energy in discrete packets • ATP,NADH + H+,FADH2 • Fatty Acid Oxidation Pathway