To determine the correct sequence of four carbon acids formed during the Krebs cycle, we can follow these steps:
### Step-by-Step Solution:
1. **Understanding the Krebs Cycle**:
- The Krebs cycle, also known as the citric acid cycle, is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetate derived from carbohydrates, fats, and proteins.
2. **Starting Point - Acetyl CoA**:
- The cycle begins with Acetyl CoA combining with oxaloacetic acid (a 4-carbon compound) to form citric acid (a 6-carbon compound).
3. **Formation of Four Carbon Compounds**:
- As the cycle progresses, citric acid undergoes a series of transformations:
- Citric acid is converted to isocitrate, then to alpha-ketoglutarate (5 carbons), and subsequently to succinyl-CoA (4 carbons).
- From succinyl-CoA, succinic acid (4 carbons) is formed.
4. **Sequence of Four Carbon Acids**:
- After succinic acid, the cycle continues with:
- **Succinic Acid** → **Fumaric Acid** → **Malic Acid** → **Oxaloacetic Acid**.
- This sequence indicates that the four carbon acids formed in order are:
- Succinic Acid
- Fumaric Acid
- Malic Acid
- Oxaloacetic Acid
5. **Identifying the Correct Option**:
- Based on the sequence derived, we can analyze the provided options:
- Option 1: Oxaloacetic acid, fumaric acid, malic acid, and succinic acid (Incorrect)
- Option 2: Oxaloacetic acid, malic acid, fumaric acid, and succinic acid (Incorrect)
- Option 3: Succinic acid, malic acid, fumaric acid, and oxaloacetic acid (Incorrect)
- Option 4: Succinic acid, fumaric acid, malic acid, and oxaloacetic acid (Correct)
### Final Answer:
The correct sequence of four carbon acids formed during the Krebs cycle is:
**Succinic Acid → Fumaric Acid → Malic Acid → Oxaloacetic Acid** (Option 4).
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