Optometry Admission Test (OAT) Practice

What key process occurs in the citric acid cycle?

1. Conversion of pyruvate to lactate

2. Formation of glucose from pyruvate

3. Entry of acetyl CoA and exit of coenzymes

4. Splitting of glucose molecules

The correct answer is: Entry of acetyl CoA and exit of coenzymes

The citric acid cycle, also known as the Krebs cycle or TCA cycle, is a crucial metabolic pathway that occurs in the mitochondria of cells. One of its key processes involves the entry of acetyl CoA, which is derived from carbohydrates, fats, and proteins through various metabolic pathways. This acetyl CoA combines with oxaloacetate to form citrate, initiating the cycle. As the cycle progresses, a series of enzymatic reactions take place that leads to the release of energy stored in the bonds of acetyl CoA. During the citric acid cycle, coenzymes such as NAD+ and FAD are reduced to NADH and FADH2, respectively. This transformation is vital as these reduced coenzymes carry high-energy electrons to the electron transport chain, leading to ATP synthesis. Additionally, carbon dioxide is released as a byproduct of this metabolic process, which is crucial for cellular respiration. The other processes mentioned in the options do not occur in the citric acid cycle: the conversion of pyruvate to lactate relates to anaerobic respiration, the formation of glucose from pyruvate is part of gluconeogenesis, and splitting of glucose molecules refers to glycolysis. These processes take place in different metabolic