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Biology Question on excretory products and their elimination

Krebs cycle begins with which of the following reaction?

A

(A) Citric acid + Acetyl CoA

B

(B) Oxaloacetic acid + Pyruvic acid

C

(C) Oxaloacetic acid + Citric acid

D

(D) Oxaloacetate + Acetyl CoA

Answer

(D) Oxaloacetate + Acetyl CoA

Explanation

Solution

Explanation:
Krebs cycle is responsible for the complete metabolism of pyruvic acid in the mitochondria. The Krebs cycle begins with condensation of two carbon unit (acetyl-CoA) with a four-carbon unit (oxaloacetate) to form a six carbon atom containing organic acid (citric acid). The enzyme catalyzing this reaction is citrate synthase. As the first stable intermediate is citric acid, this cycle is also called as citric acid. The citric acid contains three carboxylic groups. Therefore, the Krebs cycle is also called as the tricarboxylic acid cycle or TCA cycle.Hence, the correct option is (D).