Cell Respiration C 6 H 12 O O H 2 O  6 CO H 2 O + ATP

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

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

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

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

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

Glycolysis Summary: y/Biology1111/animations/glycolysis.html y/Biology1111/animations/glycolysis.html y/Biology1111/animations/glycolysis.html y/Biology1111/animations/glycolysis.html OVERALL REACTION: Biology/Bio231/glycolysis.html Biology/Bio231/glycolysis.html Biology/Bio231/glycolysis.html Biology/Bio231/glycolysis.html Glucose + 2 ATP  2 pyruvate + 2NADH + 4 ATP (net gain of 2 ATP) (net gain of 2 ATP)

Remaining Processes occur in the Mitochondria

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

Overall: 2 puruvate + 2 NAD CoA  2 puruvate + 2 NAD CoA  2 acetyl CoA + 2 NADH + 2 CO 2

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

Citric Acid Cycle

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

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

3 of the 4 complexes are proton pumps – pump H + into the intermembrane space 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 I – accepts e- from NADH and transfers it via ubiquinone (aka coenzyme Q) to Complex III Complex II – accepts e- from FADH 2 and transfers via ubiquinone Complex II – accepts e- from FADH 2 and transfers via ubiquinone

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

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

Exergonic diffusion coupled to endergonic ATP synthesis Exergonic diffusion coupled to endergonic ATP synthesis ent/movie.htm ent/movie.htm ent/movie.htm ent/movie.htm at/metabolism/atpsyn1.swf at/metabolism/atpsyn1.swf at/metabolism/atpsyn1.swf at/metabolism/atpsyn1.swf at/metabolism/atpsyn2.swf at/metabolism/atpsyn2.swf at/metabolism/atpsyn2.swf at/metabolism/atpsyn2.swf

SO WHAT’S THE POINT?? Glycolysis gives us 2 ATP (net) + 2 NADH Glycolysis gives us 2 ATP (net) + 2 NADH Pyruvate oxidation– 2 NADH + 2 CO 2 Pyruvate oxidation– 2 NADH + 2 CO 2 Citric Acid Cycle – 2 ATP + 4 CO NADH + 2FADH 2 Citric Acid Cycle – 2 ATP + 4 CO NADH + 2FADH 2

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

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

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