In the first step of the Krebs cycle, the following changes occur, EXCEPT:
Correct answer: D. Decarboxylation and condensation of Co-A
- A. Formation of citrate
- B. Condensation of oxaloacetate and acetyl Co-A
- C. Coenzyme A (CoA) is released
- D. Decarboxylation and condensation of Co-A
Explanation
The correct answer is Option D: decarboxylation and condensation of acetyl-CoA. In the first step of the Krebs cycle, acetyl-CoA combines with oxaloacetate to form citrate, a reaction catalyzed by citrate synthase. This step involves condensation but not decarboxylation. Decarboxylation occurs later in the cycle, during the conversion of isocitrate to alpha-ketoglutarate and alpha-ketoglutarate to succinyl-CoA. Therefore, Option D correctly identifies a process that does not occur in the first step of the Krebs cycle. Options A, B, and C describe processes related to the first step of the Krebs cycle.
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Cellular respiration explains how cells release energy from glucose through glycolysis, the link reaction, Krebs cycle and electron transport chain. It includes ATP production, substrate-level and oxidative phosphorylation, aerobic versus anaerobic respiration, and the roles of mitochondria, oxygen and fermentation in energy transfer.
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