Citric Acid Cycle

Question 1

What is the overall reaction equation of the CAC?

Answer 1

Acetyl-CoA + 2H20 + OH –> 2CO2 + Hs-CoA + 7H +8e

Question 2

Where do 6/8 electrons go?

Answer 2

The transfer to 3 molecules of NAD+ with 3 protons.

Question 3

Where do the remaining 2 electrons go?

Answer 3

One molecule Q with two protons.

Question 4

How many free protons are produced per pyruvate?

Answer 4

2.

Question 5

For each acetyl group that enters the pathway, what are the products?

Answer 5

2 CO2
NADH and QH2
GDP
Oxaloacetate

Question 6

What occurs in the first step of the CAC?

Answer 6

Citrate synthesis:

Acetyl CoA reacts with oxaloacetate and water to form citrate, Coenzyme A, and a proton.

Question 7

Is citrate synthesis reversible?

Answer 7

Metabolically no, due to the large free energy released to drive the reaction forward.

Question 8

What enzyme is involved in citrate synthesis?

Answer 8

Citrate synthase.

Question 9

What is citrate synthase inhibited by?

Answer 9

Increased concentrations of citrate (larger than physiologically possible).

Question 10

What is the rearrangement (2nd) step of the CAC?

Answer 10

Conversion of citrate to isocitrate.

Question 11

Is the second step of CAC reversible?

Answer 11

Yes.

Question 12

What is the third step of the CAC?

Answer 12

Dehydrogenation of isocitrate occurs in two parts.

Question 13

What occurs during the first oxidative decarboxylation step of CAC?

Answer 13

Isocitrate is oxidized, one of the hydrogens is transferred to NAD+, and one hydrogen is incorporated into the final product.

Question 14

What enzyme is activated in the first oxidative decarboxylation step of CAC?

Answer 14

Isocitrate dehydrogenase.

Question 15

Is the first oxidative decarboxylation of isocitrate reversible?

Answer 15

No, large negative free energy change.

Question 16

What occurs during the second oxidative decarboxylation step of CAC?

Answer 16

Oxalosuccinate (5C) is decarboxylated to form alpha-ketoglutarate.

Question 17

What enzyme is activated in the decarboxylation of oxalosuccine?

Answer 17

Alpha-ketoglutarate dehydrogenase.

Question 18

Is the decarboxylation of oxalosuccinate reversible?

Answer 18

No.

Question 19

What enzyme is alpha-ketoglutarate dehydrogenase similar to?

Answer 19

PDH.

Question 20

What occurs following the formation of alpha-ketoglutarate?

Answer 20

It is oxidated to succinyl-CoA, producing CO2 and NADH.

Question 21

What occurs following the formation of succinyl-CoA?

Answer 21

Succinyl CoA is converted to succinate by succinyl CoA synthase in a reversible reaction that involves the SLP of GDP.

Question 22

What occurs following the formation of succinate?

Answer 22

Succinate is oxidized reversibly into fumarate, a reaction catalyzed by succinate dehydrogenase.
Q is reduced to QH2 (integral membrane protein II)
FADH2 produced, then reoxidized when it transfers protons to Q.

Question 23

What is succinate dehydrogenase a part of?

Answer 23

Membrane bound enzyme part of complex II.

Question 24

What occurs following the formation of fumarate?

Answer 24

Hydration of fumarate to synthesize malate. Reversible reaction.

Question 25

What occurs following the formation of malate?

Answer 25

Oxidation of malate to regenerate oxaloacetate and a molecule of NADH.

Question 26

Is the formation of oxaloacetate reversible?

Answer 26

Yes.

Question 27

Are there any rate limiting steps in CAC?

Answer 27

No because it is cyclical.

Question 28

How is the CAC regulated?

Answer 28

Inhibited by NADH/ATP | Activated by Calcium and ADP.

Question 29

What enzymes of the CAC are regulated?

Answer 29

The oxidative decarboxylators; Isocitrate decarboxylase Alpha-ketoglutarate dehydrogenase

Question 30

What can CAC intermediates be used in? Why is this relevant?

Answer 30

Synthesis of amino acids, carbohydrates, fats, etc. | It is amphibolic (catabolic and anabolic)

Question 31

What are anaplerotic reactions?

Answer 31

Reactions that replenish intermediates of cyclic metabolite pathways.

Question 32

What reaction is anaplerotic?

Answer 32

Pyruvate carboxylase enzyme catalyzes the formation of ozaloacetate.

Question 33

How is pyruvate carboxylase regulated?

Answer 33

Activated by Acetyl-CoA | Inhibited by ADP.

Question 34

How many ATP are generated per acetyl-CoA?

Answer 34

~10; 7.5/3NADH 1.5/1FADH 1 GTP

Question 35

How many ATP does the complete aerobic oxidation of glucose yield?

Answer 35

32 ATP

Question 36

What reactions link the CAC to glycolysis?

Answer 36

Pyruvate dehydrogenation

Question 37

What reactions are decarboxylation?

Answer 37

Isocitrate to alpha-ketoglutarate Alpha-ketoglutarate to succinyl CoA Pyruvate to Acetyl-CoA

Question 38

What are the energy capture steps?

Answer 38

``` Isocitrate to alpha-ketoglutarate Alpha-keto glutamate to succinyl CoA Succinyl CoA to Succinate Succinate to fumarate Malate to Oxaloacetate ```

Question 39

What reactiosn are regulated?

Answer 39

Isocitrate to alpha-ketoglutarate Alpha-keto glutamate to succinyl CoA PDH

Question 40

How much ATP is produced by the oxidation of one molecule lactate?

Answer 40

15 ATP