Question

Which one of the following metabolites is common to respiration mediated breakdown of fats, carbohydrates and proteins?

• A. Glucose-6-phosphate
• B. Fructose-1, 6-bisphosphate
• C. Pyruvic acid
• D. Acetyl CoA

Answer 1

The correct option is D Acetyl CoA

Carbohydrates are the preferred substrates for respiration. Glucose among them is the most preferred. All the carbohydrates are primarily converted into glucose before being used as substrate. Other substrates like fats and proteins can also be used but conditionally. If they are used as substrates, they do not enter the respiratory pathway at the first step.

Fats have to be broken down into fatty acids and glycerol. Fatty acids have to be converted into acetyl CoA to enter the respiratory pathway.

Proteins have to be broken down into amino acids. Amino acids have to undergo deamination to form organic acids which can enter the steps in Krebs cycle. The organic acid produced may also be pyruvate, which can then be converted into acetyl CoA to enter the pathway.

Thus we see that acetyl CoA is the common intermediate to respiration mediated breakdown of fats, carbohydrates and proteins.