Citric Acid Cycle 1

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Citric Acid Cycle 1. C483 Spring 2013. 1. The net effect of the eight steps of the citric acid cycle is to A) completely oxidize an acetyl group to carbon dioxide. B) convert pyruvate to Acetyl CoA. C) produce a citrate molecule D) produce 8 ATP for every pass through the cycle . - PowerPoint PPT Presentation


Citric Acid Cycle 1

Citric Acid Cycle 1C483 Spring 20131. The net effect of the eight steps of the citric acid cycle is toA) completely oxidize an acetyl group to carbon dioxide.B) convert pyruvate to Acetyl CoA.C) produce a citrate moleculeD) produce 8 ATP for every pass through the cycle.E) More than one of the above

2. The order of prosthetic groups as they act in the three proteins of the PDH(pyruvate dehydrogenase) complex is:A) FAD thiamine pyrophosphate NAD+B) FAD thiamine pyrophosphate dihydrolipoamideC) thiamine pyrophosphate dihydrolipoamide FADD) NAD+ FAD dihydrolipoamide

3. Which might you expect to have a higher than normal blood concentration in an individual with thiamine deficiency? A) Isocitrate. B) Pyruvate. C) Oxaloacetate. D) Acetyl CoA.

4. About how many total ATP equivalents are generated by the complete oxidation of one molecule of acetyl CoA?A) 1.5B) 2.5C) 3D) 10E) 305. Which product of the citric acid cycle produces the most ATP equivalents?A) NADH.B) QH2.C) GTP.D) CO2.

OverviewCompartmentalizationGlycolysis: CytosolCitric Acid Cycle: mitochondria

OverviewGlycolysisPyruvate dehydrogenase complexCommitment of carbon away from carbohydratesCitric acid cycle

Pyruvate Dehydrogenase ComplexThree distinct enzymesin a massive complexFive chemical stepsWhat cofactors needed?

Pyruvate Dehydrogenase (E1)TPP cofactor: draw mechanism of decarboxylation

Dihydrolipoamide Acyltransferase (E2)Transfer catalyzed by E1Mechanism of redox

Step 3: transferMaintenance of high energy bondAcetyl CoA product is madeLipoamide still reducednot catalytically viable at this point

Dihydrolipoamide dehydrogenase (E3)Redox of prosthetic FAD/FADH2Still not a regenerated catalyst!

Step 5: NADH producedProsthetic group is restoredStep 1 uses proton, step 5 regeneratesOxidation of one carbon atom used toProduce high energy thioesterProduce NADH

Overall Reaction

Fate of Acetyl CoACitric Acid Cycle (in muscle)energy production (high potential electrons)

Other tissues use intermediates in many waysAmphibolic

Citric Acid Cycle

Major points: carbon cycle, reaction types, reaction logic, energy harvest, selected enzyme reactionsMinor points: enzyme names, substrate names, order of reactions

Energy FlowDecarboxylation or alcohol oxidation = NADHDouble bond formation = QH2DehydrogenasesHigh energy bond = substrate phosphorylation

ATP Harvest: Net equations

Net ATP Harvest from GlucoseGlycolysis = 2 ATPPlus 3 or 5 ATP from NADHIn humans, cytosolic NADH leads to production of 3 ATPPyruvate DH = 5 ATPCitric Acid Cycle = 20 ATPTotal: 30 ATP/glucose in humans