Question

In respiration, pyruvic acid is
A) Formed only when oxygen is available
B) One of the products of Krebs cycle
C) Broken down into two carbon fragments and carbon dioxide
D) A result of the protein breakdown

Answer 1

Hint: The process of aerobic respiration occurs in three different stages – the first one – Glycolysis; the second one – Kreb’s Cycle; and the third one – Electron Transport System.

Complete Answer:
- The last stage of glycolysis yields a 3C compound known as pyruvic acid. This pyruvic acid may further undergo anaerobic respiration if there is no oxygen present within the cell.
- However, if the oxygen is present, the pyruvate finds an easy entry into the Krebs Cycle.
- This entry is facilitated through the oxidative decarboxylation in the presence of the enzyme complex namely pyruvate dehydrogenase. This reaction works as the linking reaction between Glycolysis and Kreb’s Cycle.
- As a result of this decarboxylation process, pyruvic acid results in the formation of Acetyl CoA which is a 2C compound thereby resulting in the release of carbon dioxide.

Option A: There is no role of the oxygen for the production of the pyruvic acid. Thus, this is an incorrect option for the given question.
Option B: Pyruvic acid is one of the products of Glycolysis and it enters Krebs Cycle in its whole form. Thus, this is an incorrect option for the given question.
Option C: During aerobic respiration, the pyruvic acid molecule is broken down into two different carbon fragments thereby releasing carbon dioxide. Thus, this is a correct option for the given question.
Option D: Proteins break down into amino acids as they are prime constituents of any protein. As pyruvic acid is not an amino acid, this is an incorrect option for the given question.

Thus, the correct option for the given question is Option C i.e. broken down into two carbon fragments and carbon dioxide.

Note: Pyruvic acid through the Citric Acid Cycle supplies energy to the living cells in presence of oxygen. When oxygen is absent, the pyruvic acid undergoes fermentation to release lactic acid.