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 .

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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.

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 → dihydrolipoamide

C) thiamine pyrophosphate → dihydrolipoamide → FAD

D) 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) 1.5

B) 2.5

C) 3

D) 10

E) 30

5. Which product of the citric acid cycle produces the most ATP equivalents?

A) NADH.

B) QH2.

C) GTP.

D) CO2.


Overview

  • Compartmentalization

    • Glycolysis: Cytosol

    • Citric Acid Cycle: mitochondria


Overview

  • Glycolysis

  • Pyruvate dehydrogenase complex

    • Commitment of carbon away from carbohydrates

  • Citric acid cycle


Pyruvate Dehydrogenase Complex

  • Three distinct enzymes—in a massive complex

  • Five chemical steps

  • What cofactors needed?


Pyruvate Dehydrogenase (E1)

  • TPP cofactor: draw mechanism of decarboxylation


DihydrolipoamideAcyltransferase (E2)

  • Transfer catalyzed by E1

  • Mechanism of redox


Step 3: transfer

  • Maintenance of high energy bond

  • Acetyl CoA product is made

  • Lipoamide still reduced—not catalytically viable at this point


Dihydrolipoamide dehydrogenase (E3)

  • Redox of prosthetic FAD/FADH2

  • Still not a regenerated catalyst!


Step 5: NADH produced

  • Prosthetic group is restored

  • Step 1 uses proton, step 5 regenerates

  • Oxidation of one carbon atom used to

    • Produce high energy thioester

    • Produce NADH


Overall Reaction


Fate of Acetyl CoA

  • Citric Acid Cycle (in muscle)—energy production (high potential electrons)

  • Other tissues use intermediates in many ways

    • Amphibolic


Citric Acid Cycle

  • Major points: carbon cycle, reaction types, reaction logic, energy harvest, selected enzyme reactions

  • Minor points: enzyme names, substrate names, order of reactions


Energy Flow

  • Decarboxylation or alcohol oxidation = NADH

  • Double bond formation = QH2

  • Dehydrogenases

  • High energy bond = substrate phosphorylation


ATP Harvest: Net equations


Net ATP Harvest from Glucose

  • Glycolysis = 2 ATP

    • Plus 3 or 5 ATP from NADH

    • In humans, cytosolic NADH leads to production of 3 ATP

  • Pyruvate DH = 5 ATP

  • Citric Acid Cycle = 20 ATP

  • Total: 30 ATP/glucose in humans


Answers

  • A

  • C

  • B

  • D

  • A


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