Which step is called gateway step/link reaction in aerobic respiration?

Options

A. Glycolysis
B. Formation of acteyl coenzyme A
C. Citric acid formation
D. ETS terminal oxidation

Answer

### Step-by-Step Solution:

1. **Understanding Aerobic Respiration**: Aerobic respiration consists of several steps, including glycolysis, the link reaction (gateway step), and the TCA (Krebs) cycle.

2. **Identifying Glycolysis**: The first step in aerobic respiration is glycolysis, where glucose is broken down into two molecules of pyruvate.

3. **Recognizing the Link Reaction**: The link reaction connects glycolysis to the TCA cycle. It serves as a bridge between these two metabolic pathways.

4. **Formation of Acetyl Coenzyme**: In the link reaction, the pyruvate produced from glycolysis is transported into the mitochondrial matrix, where it is converted into acetyl coenzyme A (acetyl CoA).

5. **Enzyme Involvement**: The enzyme responsible for this conversion is called the pyruvate dehydrogenase complex.

6. **Conclusion**: The link reaction is crucial because it transforms the end product of glycolysis (pyruvate) into a substrate that enters the TCA cycle (acetyl CoA). Therefore, the step that is referred to as the gateway step or link reaction in aerobic respiration is the formation of acetyl coenzyme A from pyruvate.

### Final Answer:
The step called the gateway step or link reaction in aerobic respiration is the formation of acetyl coenzyme A from pyruvate.

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