TCA cycle

Question 1

What is the primary driving factor for the TCA cycle?

Answer 1

The rate of ATP production

Look at ATP/ADP ratio and NADH/NAD+ ratio

Question 2

Give an example of regulation of the TCA cycle which involved one of the early irreversible steps

Answer 2

Isocitrate dehydrogenase is allosterically inhibited by the high-energy signal NADH and activated but the low energy signal ADP

Question 3

By the end of stage 3 of catabolism what has occurred in terms of glucose breakdown? (2)

Answer 3

• all C-C bonds have been broken and the carbons oxidised to CO2
• all the C-H. Bond have been broken and the H atoms transferred to NAD+ and FAD

Question 4

Where has all the energy released from glucose in the metabolism of it gone at the end of stage 3 of catabolism? (2)

Answer 4

ATP and GTP formation (2 in glycolysis and 2 in the TCA cycle)

Chemical bond energy of the e- in NADH and FAD2H

Question 5

For every molecule of glucose what are the products of the TCA cycle?

Answer 5

6 NADH
2 FADH2
2 GTP

Question 6

How is the TCA cycle regulated?

Answer 6

By energy availability ie ATP/ADP ratio and NADPH/NAD+ ratio

Question 7

The enzyme isocitrate dehydrogenase catalyses one of the reactions in the TCA cycle. It is responsible for the oxidation of NAD+ to NADH. What substances would activate and inhibit this enzyme? Why?

Answer 7

+ adp (becuase its a low energy signal)

• NADH, ATP (because of product inhibition and atp is a high energy molecule )