Citric Acid Cycle

Question 1

Citric Acid Cycle

Answer 1

An 8=step process providing energy in aerobic conditions by donating electrons from NADH to FAD, which donate electrons to the ETC.

Question 2

What happens in each step of CAC?

Answer 2

A coenzyme like NADH of FADH2 is reduced.

Question 3

What do NADH and FADH2 contribute to?

Answer 3

The ETC thus most ATP production in humans.

Question 4

Why is Acetyl CoA important in the CAC?

Answer 4

It is a significant carbon input

Question 5

Where does acetyl-CoA derive from?

Answer 5

Glucose, fatty acids but mostly glucose-derived pyruvate.

Question 6

What facilitates conversion of pyruvate to acetyl CoA?

Answer 6

Pyruvate Dehydrogenase Complex

Question 7

Pyruvate Dehydrogenase Complex

Answer 7

An enzyme complex in CAC catalyzing oxidative decarboxylation of pyruvate to acetyl-CoA, NADH and CO2

Question 8

What does PDC do generally?

Answer 8

Link the glycolytic pathway to CAC, regulating metabolism of pyruvate to maintain glucose homeostasis.

Question 9

How does covalent modificaiton regulate PDC?

Answer 9

Phosphorylation of PDC first subunit pyruvate decarboxylate, reducing PDC activity.

Question 10

What happens to Acetyl-CoA after synthesis from PDC?

Answer 10

Enters CAC

Question 11

What does CAC ultimately result in?

Answer 11

Release of two CO2 through oxidation of acetyl group, and reducition of NADH, GTP and FADH2 in every step.

Question 12

What is the first step in Citric Acid Cycl?

Answer 12

Citrate synthase catalyses condensation reaction of acetyl CoA and ocaloacetate, to form citrate.

Question 13

What is the second step of the Citric Acid Cycle?

Answer 13

Citrate is isomerised by aconitase, forming isocitrate.

Question 14

What is the third step of citric acid cycle?

Answer 14

Isocitrate is oxidatively decarboxylated by isocitrate dehydrogenase, releasing CO2 and alpha-ketoglutarate.

Question 15

What is the fourth step of Citric Acid Cycle?

Answer 15

Alpha-ketoglutarate by the AKDC, forming succinyl-CoA, producing NADH.

Question 16

What is the fifth step of the Citric Acid Cycle?

Answer 16

Succinyl CoA is cleaved by succinate thiokinase, forming succinate and GTP.

Question 17

What is the sixth step of the Citric Acid Cycle?

Answer 17

Succinate is oxidised to fumarate by succinate dehydrogenase, producing reduced FADH2 from FAD

Question 18

What is the seventh step of the Citric Acid Cycle?

Answer 18

Fumarase oxidises fumarate to form malate

Question 19

What is the eight step of the Citric Acid Cycle?

Answer 19

Malate is oxidised by malate dehydrogenase to form oxaloacetate.

Question 20

isocitrate dehydrogenase

Answer 20

This catalyses oxidative decarboxylation of isocitrate into CO2 and alpha-ketoglutarate.

Question 21

What is the mechanism of alpha-ketoglutarate decarboxylation?

Answer 21

E1 decarboxylates alpha-ketoglutarate, transferring four carbons to thiamine pyrophosphate cofactor, where then E2 transfers the succinyl group to CoASH, with assistnace form FAD, then E3 synthesises FAD along with NADH from NAD+ so that the dehydrogenase complex maintains the substrates and cofactors for continued reacitons.

Question 22

What citric acid cycle steps are irreversible?

Answer 22

citrate synthase, isocitrate dehydrogenase and α-ketoglutarate dehydrogenase.