Consider the first reaction of TCA cycle.
Acetyl `CoA+OA A+H_(2)O overset("Citrate synthase")to`
`" " (A)+CoA.`
What is true about compound A?

Options

A. First product of TCA cycle
B. Tricarboxylic acid and six carbon compound
C. It undergoes recorganization in the presence of enzyme aconitase to form cis-aconitate
D. All of these

Answer

To solve the question regarding compound A in the first reaction of the TCA cycle, we will follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**: The first reaction of the TCA cycle involves acetyl CoA and oxaloacetate (OAA) reacting in the presence of the enzyme citrate synthase, along with water.

2. **Understand the Reaction**: The reaction can be summarized as:
\[ \text{Acetyl CoA} + \text{OAA} + \text{H}_2\text{O} \overset{\text{Citrate synthase}}{\rightarrow} \text{Compound A} + \text{CoA} \]
Here, acetyl CoA (a 2-carbon molecule) combines with oxaloacetate (a 4-carbon molecule) to form compound A.

3. **Determine the Product**: When acetyl CoA (2 carbons) and oxaloacetate (4 carbons) combine, they form citrate, which is a 6-carbon compound. Therefore, compound A is citrate.

4. **Characterize Compound A (Citrate)**:
- **First Product of TCA Cycle**: Citrate is indeed the first product formed in the TCA cycle.
- **Carboxylic Acid**: Citrate is a tricarboxylic acid, meaning it has three carboxyl (-COOH) groups.
- **Carbon Count**: Citrate contains 6 carbon atoms.

5. **Conclusion**: Based on the above points, we can conclude that compound A is citrate, and it possesses the following characteristics:
- It is the first product of the TCA cycle.
- It is a tricarboxylic acid.
- It is a 6-carbon compound.

### Final Answer:
Compound A is citrate, which is the first product of the TCA cycle, a tricarboxylic acid, and contains 6 carbon atoms.

---