The TCA cycle starts with the condensation of acetyl group with oxaloacetic acid and water to yield citric acid. The reaction is catalysed by the enzyme

Options

A. Citrate decarboxylase
B. Citrate dehydrogenase
C. Citrate synthase
D. Both A and B

Explanation

To answer the question regarding the enzyme that catalyzes the reaction in the TCA cycle where the acetyl group condenses with oxaloacetic acid and water to yield citric acid, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the TCA Cycle**: The TCA cycle, also known as the Krebs cycle or citric acid cycle, is a crucial metabolic pathway that plays a significant role in cellular respiration. It involves a series of chemical reactions used by all aerobic organisms to generate energy.

2. **Identifying the Reactants**: The initial reaction of the TCA cycle involves the condensation of an acetyl group (derived from acetyl-CoA) with oxaloacetic acid (OAA) and water.

3. **Formation of Citric Acid**: When the acetyl group combines with oxaloacetic acid, it forms citric acid (also known as citrate). This is the first step in the TCA cycle.

4. **Enzyme Involved**: The reaction that catalyzes the formation of citric acid from acetyl-CoA and oxaloacetic acid is facilitated by a specific enzyme.

5. **Naming the Enzyme**: The enzyme responsible for this reaction is called **citrate synthase**. It catalyzes the condensation of acetyl-CoA and oxaloacetic acid to produce citric acid.

### Final Answer:
The reaction is catalyzed by the enzyme **citrate synthase**.

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