Cellular Respiration

Question 1

Enzyme that catalyses the reaction in which pyruvate is converted into acetyl-CoA.

Answer 1

pyruvate dehydrogenase complex

Question 2

What are the three subunits of pyruvate dehydrogenase complex?

Answer 2

E1: Thiamine pyrophosphate (TTP)
E2: Coenzyme A (CoA-SH) and lipoic acid
E3: FAD and NAD

Question 3

Describe the overall enzymatic activity of the pyruvate dehydrogenase complex.

Answer 3

E1 has dehydrogenase activity
E2 has transacetylase activity
E3 has dehydrogenase activity

Question 4

Describe what happens in E1 of pyruvate dehydrogenase complex

Answer 4

The first is decarboxylation of pyruvate in which the thiazolium ring of TTP attacks the carbonyl group of pyruvate which then releases CO2 and form hydroxyethyl TTP.

Question 5

Describe what happens in E2 of pyruvate dehydrogenase complex

Answer 5

First, lipollysine is reduced. The hydroxyethyl group of TTP is oxidized to transacyl and is then transferred onto the reduced form of lipollysine to form acyl lipollysine.
Second, the acyl group of acyl lipollysine is transferred onto coenzyme-A to form acetyl-CoA.
Third, the reduced form of lipollysine is oxidized by FAD+

Question 6

Describe what happens in E3 of pyruvate dehydrogenase complex

Answer 6

1. FAD+ picks up the two electrons (of the reduced form of lipollysine) to form FADH2.
2. FADH2 transfers the two protons onto NAD+ to form NADH and H+

Question 7

How is the pyruvate dehydrogenase complex regulted?

Answer 7

It’s activated by AMP, CoA-SH, NAD+ and Ca2+
It’s inhibited by ATP, acetyl-CoA, NADH, and fatty acids.

Question 8

How is the pyruvate dehydrogenase complex regulated through covalent modifications?

Answer 8

High levels of glucose in the body will stimulate insulin signaling which will activate PP1. PP1 will dephosphorylate pyruvate dehydrogenase phosphatase to active it.
Pyruvate dehydrogenase kinase is not response to glucagon, but it is inactivated in the presence of ATP through phosphorylation.