Citric acid is formed in Krebs cycle by the combination of oxaloacetate with

Options

A. OAA
B. Acetyl CoA
C. Malic acid
D. Pyruvic acid

Answer

To answer the question "Citric acid is formed in the Krebs cycle by the combination of oxaloacetate with," we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Components**:
- Understand that citric acid (also known as citrate) is formed in the Krebs cycle.
- Recognize that oxaloacetate (or oxaloacetic acid) is a 4-carbon compound.

**Hint**: Remember that oxaloacetate is a key player in the Krebs cycle.

2. **Know the Reactants**:
- The question asks what combines with oxaloacetate to form citric acid.
- The relevant reactant here is acetyl coenzyme A (acetyl CoA), which is a 2-carbon compound produced from the link reaction.

**Hint**: Think about the source of acetyl CoA and its role in the Krebs cycle.

3. **Reaction Process**:
- The reaction occurs when acetyl CoA combines with oxaloacetate.
- This reaction is catalyzed by the enzyme citrate synthase.

**Hint**: Enzymes are crucial for facilitating biochemical reactions; remember the name of the enzyme involved.

4. **Formation of Citric Acid**:
- When acetyl CoA (2 carbons) reacts with oxaloacetate (4 carbons), they form citric acid (6 carbons).
- This is the first step of the Krebs cycle.

**Hint**: Visualize the carbon count: 2 (from acetyl CoA) + 4 (from oxaloacetate) = 6 (in citric acid).

5. **Evaluate the Options**:
- The correct answer to the question is that oxaloacetate reacts with acetyl coenzyme A to form citric acid.
- Other options provided (like oxaloacetate with itself, malic acid, or pyruvic acid) are incorrect.

**Hint**: Always cross-check the options against the known biochemical pathways.

### Final Answer:
Citric acid is formed in the Krebs cycle by the combination of oxaloacetate with acetyl coenzyme A.