In Kreb's cycle

Options

A. Acetyl coenzyme A undergoes 4 oxidations and 2 decarboxylations
B. Pyruvic acid undergoes 4 oxidations and 2 decarboxylations
C. TCA undergoes 4 oxidations and 4 decarboxylations
D. OAA undergoes 4 oxidations and 2 decarboxylations

Answer

### Step-by-Step Solution for the Question on Kreb's Cycle

1. **Understanding the Kreb's Cycle**: The Kreb's cycle, also known as the citric acid cycle or TCA cycle, is a series of biochemical reactions that take place in the matrix of mitochondria. It is crucial for aerobic respiration and involves the oxidation of acetyl CoA derived from carbohydrates, fats, and proteins.

2. **Components of the Cycle**: The cycle begins with acetyl CoA (a two-carbon molecule) combining with oxaloacetate (a four-carbon molecule) to form citrate (a six-carbon molecule). This is the first step of the cycle.

3. **Steps of the Cycle**: The Kreb's cycle consists of eight steps:
- **Step 1**: Acetyl CoA combines with oxaloacetate to form citrate (condensation).
- **Step 2**: Citrate is converted to isocitrate via the enzyme aconitase.
- **Step 3**: Isocitrate is oxidized to alpha-ketoglutarate, releasing CO2 (decarboxylation).
- **Step 4**: Alpha-ketoglutarate is converted to succinyl CoA, releasing another CO2 (decarboxylation).
- **Step 5**: Succinyl CoA is converted to succinate.
- **Step 6**: Succinate is oxidized to fumarate.
- **Step 7**: Fumarate is converted to malate.
- **Step 8**: Malate is oxidized back to oxaloacetate.

4. **Counting Oxidation and Decarboxylation Steps**:
- **Oxidation Steps**: The steps that involve the oxidation of substrates are the conversion of succinate to fumarate, fumarate to malate, and malate to oxaloacetate. This gives us a total of **4 oxidation steps**.
- **Decarboxylation Steps**: The steps that involve the removal of carbon dioxide (decarboxylation) are the conversion of isocitrate to alpha-ketoglutarate and alpha-ketoglutarate to succinyl CoA. This gives us a total of **2 decarboxylation steps**.

5. **Conclusion**: Therefore, in the Kreb's cycle, acetyl CoA undergoes **4 oxidations** and **2 decarboxylations**. The correct answer to the question is **Option A**.