Question

The very first step in the formation of acetyl CoA is the
A. Formation of a complex between thiamine pyrophosphate and Pyruvate
B. Release of the acetyl group from liquid acid to CoA
C. Decarboxylation of pyruvate
D. Transfer of electrons from reduced lipoic acid to NAD

Answer 1

Hint: Glycolysis occurring in the mitochondrial matrix is responsible for Acetyl-CoA generation. This Acetyl CoA enters the kreb cycle where it undergoes oxidation thus producing energy.

Complete answer:
Pyruvate is converted into acetyl-CoA (acetyl coenzyme A) with the help of the enzyme complex called pyruvate dehydrogenase complex. This reaction is known as oxidation of pyruvate or decarboxylation of pyruvate. This is the step connecting the glycolysis and the Krebs cycle therefore it is also known as link reaction. In a glycolytic reaction, a 6C molecule of glucose is split into 2 molecules of 3C pyruvates. So, the link reaction occurs two times repeatedly to produce 2 molecules of acetyl CoA. This acetyl CoA then enters the Krebs cycle. In proteins, various biochemical reactions are carried out by acetyl coenzyme A. Also, lipid and carbohydrate metabolism also needs participation of this acetyl coenzyme A. However, the major function of acetyl coenzyme A is to provide the acetyl group to the Krebs cycle (also known as citric acid cycle) where it can be oxidized to produce energy.

So, the correct answer is option “C”. That is the very first step in the formation of acetyl CoA is the decarboxylation of pyruvate.

Note: β-mercaptoethylamine group is linked to the pantothenic acid (vitamin B5) via amide linkage and 3' phosphorylated Adenosine diphosphate (ADP) to form Coenzyme A (also written as CoA or CoASH). Further acetylation of this coenzyme A is carried out through glycolysis (breakdown of carbohydrates) and β-oxidation (breakdown of fatty acids). This acetylated coenzyme A then enters the kreb cycle. In this cycle, oxidation of this acetyl coenzyme A to carbon dioxide and water takes place.