Cell Respiration

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Cell Respiration

• C6H12O6 6 O2 6 H2O ? 6 CO2 12 H2O ATP

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Overview 4 main processes

• Glycolysis
• Pyruvate oxidation
• Citric Acid Cycle
• Electron Transport Chain

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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

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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

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• 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

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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- P is
  transferred from intermediate to ADP
• 2x per G3P
• Total of 4 ATP made

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Glycolysis Summary

• http//programs.northlandcollege.edu/biology/Biolo
  gy1111/animations/glycolysis.html
• OVERALL REACTION
• http//www.science.smith.edu/departments/Biology/B
  io231/glycolysis.html
• Glucose 2 ATP ? 2 pyruvate 2NADH 4 ATP
• (net gain of 2 ATP)

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Remaining Processes occur in the Mitochondria
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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

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Overall

• 2 puruvate 2 NAD 2 CoA ?
• 2 acetyl CoA 2 NADH 2 CO2

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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

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Citric Acid Cycle
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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

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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.

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• 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

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• 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

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• http//www.science.smith.edu/departments/Biology/B
  io231/etc.html
• http//highered.mcgraw-hill.com/sites/0072437316/s
  tudent_view0/chapter9/animations.html
• http//www.stolaf.edu/people/giannini/flashanimat/
  metabolism/mido20e20transport.swf

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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

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• 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

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SO WHATS 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

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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

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GRAND TOTALS

• Glycolysis 2 ATP
• Citric Acid Cycle 2 ATP
• ETC 32 34 ATP
• Aerobic Respiration 36 38 ATP

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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