Lecture 27: TCA Cycle

Question 1

E1 of PDH Complex

Answer 1

Prosthetic group: TPP
Reaction catalyzed: Oxidative decarboxylation of pyruvate
Subunits: 24

Question 2

E2 of PDH Complex

Answer 2

Prosthetic group: Lipoamide
Reaction catalyzed: Transfer of acetyl group to CoA
Subunits: 24

Question 3

E3 of PDH Complex

Answer 3

Prosthetic group: FAD
Reaction catalyzed: Regeneration of oxidized lipoamide
Subunits: 12

Question 4

Name the stoichiometric cofactors involved in making Acetyl CoA from pyruvate via PDH complex

Answer 4

CoA, NAD+

Question 5

How is pyruvate dehydrogenase regulated?

Answer 5

1. Allosterically by reverse phosphorylation (PDH is OFF when phosphorylated) - stimulated by products
2. High [Acetyl CoA] directly inhibits E2
3. Accumulation of ADP, pyruvate activate phosphatases

Question 6

Which enzyme catalyzes the first step in the TCA cycle?

Answer 6

Citrate synthase

Question 7

What are the substrates and products for the alpha-ketoglutarate dehydrogenase step of TCA?

Answer 7

Substrates: alpha-ketoglutarate, NAD+, CoA
Products: Succinyl CoA, CO2, NADH

Question 8

What major control point/rate limiting step of TCA cycle occurs just upstream of alpha-ketoglutarate?

Answer 8

Isocitrate dehydrogenase

Question 9

How is isocitrate dehydrogenase regulated?

Answer 9

1. Allosterically stimulated by ADP

2. Inhibited by ATP and NADH

Question 10

Which step of the TCA cycle yields GTP?

Answer 10

Succinyl CoA synthetase step