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Cell Respiration

Cell Respiration. C 6 H 12 O 6 + 6 O 2 + 6 H 2 O  6 CO 2 + 12 H 2 O + ATP. Overview: 4 main processes. Glycolysis Pyruvate oxidation Citric Acid Cycle Electron Transport Chain. Glycolysis. “Sugar splitting” – 1 molecule of glucose (6-C) is split into 2 pyruvates (3-C)

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Cell Respiration

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  1. Cell Respiration C6H12O6 + 6 O2+ 6 H2O  6 CO2 + 12 H2O + ATP

  2. Overview: 4 main processes • Glycolysis • Pyruvate oxidation • Citric Acid Cycle • Electron Transport Chain

  3. Glycolysis • “Sugar splitting” – 1 molecule of glucose (6-C) is split into 2 pyruvates (3-C) • Occurs in cytosol • ATP, NAD+, and Pi float freely • Series of reactions catalyzed by specific enzymes

  4. 1st phase of Glycolysis is Endergonic • Requires input of ATP • Glucose is stable, not readily broken down • 2 phosphorylation rxns. transfer P from ATP to sugar  fructose 1,6-biphosphate

  5. Fructose 1,6-biphosphate broken down into 2 3-C molecules: dihydroxyacetone phosphate and glyceraldehyde-3-phosphate (G3P) • Dihydroxyacetone phosphate converted to G3P • OVERALL: Glucose + 2ATP  2 G3P + 2 ADP

  6. 2nd phase of Glycolysis is Exergonic • G3P is oxidized to produce NADH + H+ • Since 2 G3P, 2 NADH are produced (used later to produce ATP) • Substrate-level phosphorylation- Pis transferredfrom intermediate to ADP • 2x per G3P • Total of 4 ATP made

  7. Glycolysis Summary: • http://programs.northlandcollege.edu/biology/Biology1111/animations/glycolysis.html OVERALL REACTION: • http://www.science.smith.edu/departments/Biology/Bio231/glycolysis.html Glucose + 2 ATP  2 pyruvate + 2NADH + 4 ATP (net gain of 2 ATP)

  8. Remaining Processes occur in the Mitochondria

  9. Pyruvate Oxidation • Pyruvate enter mitochondria in eukaryotes • Pyruvate Dehydrogenase catalyses oxidative decarboxylation • Carboxyl removed as CO2 • 2-C fragment becomes oxidized creating NADH • 2-C acetyl group attached to coenzyme A

  10. Overall: • 2 puruvate + 2 NAD+ + 2 CoA  2 acetyl CoA + 2 NADH + 2 CO2

  11. Citric Acid Cycle • 1st reaction: acetyl CoA transfers 2-C acetyl group to 4-C oxaloacetate to get citrate • Series of reactions: • 2 CO2 are removed yielding 4-C compound • Oxidation occurs yielding 3 NADH and 1 FADH2 per acetyl coA • 1 ATP produced by substrate level phosphorylation • Oxaloacetate is regenerated

  12. Citric Acid Cycle

  13. Electron Transport Chain • ETC is series of electron carriers embedded in inner mitochondrial membrane of eukaryotes (plasma membrane of prokaryotes) • Electrons produced during glycolysis, pyruvate oxidation, and Citric Acid Cycle enter ETC via carrier molecules

  14. Overview of ETC: • High energy electrons are passed along ETC in series of exergonic reactions • Energy from these rxns. drives ATP synthesis (endergonic) • This is oxidative phosphorylation – result of redox rxns.

  15. 3 of the 4 complexes are proton pumps – pump H+ into the intermembrane space • Complex I – accepts e- from NADH and transfers it via ubiquinone (aka coenzyme Q) to Complex III • Complex II – accepts e- from FADH2 and transfers via ubiquinone

  16. Complex III – accepts e- from ubiquinone and transfers them via cytochrome c to Complex IV • Final Electron acceptor is Oxygen (1/2 O2) – it accepts 2 e- and combines with 2 protons to create water • Aerobic respiration – requires O2; without it as final e- acceptor, entire chain backs up

  17. http://www.science.smith.edu/departments/Biology/Bio231/etc.htmlhttp://www.science.smith.edu/departments/Biology/Bio231/etc.html • http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter9/animations.html# • http://www.stolaf.edu/people/giannini/flashanimat/metabolism/mido%20e%20transport.swf

  18. Chemiosmosis • ETC is coupled to ATP synthesis by proton gradient • Concentration of H+ in intermembrane space is much higher than matrix • H+ diffuses down its gradient through ATP synthase - exergonic

  19. Exergonic diffusion coupled to endergonic ATP synthesis • http://vcell.ndsu.nodak.edu/animations/atpgradient/movie.htm • http://www.stolaf.edu/people/giannini/flashanimat/metabolism/atpsyn1.swf • http://www.stolaf.edu/people/giannini/flashanimat/metabolism/atpsyn2.swf

  20. SO WHAT’S THE POINT?? • Glycolysis gives us 2 ATP (net) + 2 NADH • Pyruvate oxidation– 2 NADH + 2 CO2 • Citric Acid Cycle – 2 ATP + 4 CO2 + 6 NADH + 2FADH2

  21. ADDING UP ATP • Each NADH yields 3 ATP, so • Glycolysis – 2 NADH  6 ATP • **except for most eukaryotic cells which shuttle e- of NADH across mit. Mem., costing 1 ATP/NADH • Pyruvate oxidation – 2 NADH  6 ATP • Citric Acid Cycle – 6 NADH  18 ATP • Each FADH2 yields 2 ATP • Citric Acid Cycle – 2 FADH2 4 ATP

  22. GRAND TOTALS… • Glycolysis = 2 ATP • Citric Acid Cycle = 2 ATP • ETC = 32 – 34 ATP • Aerobic Respiration = 36 – 38 ATP

  23. Efficiency (i.e., thermodynamics) • Burning glucose releases 686 kcal/mol heat • Free energy in phosphate bonds of ATP = 7.6 kcal • 7.6 kcal/mol ATP x 36 ATP = 274 kcal/mol • Efficiency of aerobic resp. = 274/686 = 40% • Rest is lost as heat

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