Krebs' cycle is completed with the formation of

Options

A. (a) citric acid
B. (b) OAA
C. (c) succinic acid
D. (d) malic acid

Answer

**Step-by-Step Solution:**

1. **Understanding the Krebs Cycle**: The Krebs cycle, also known as the citric acid cycle or TCA cycle, is a series of biochemical reactions used by all aerobic organisms to generate energy through the oxidation of acetate derived from carbohydrates, fats, and proteins.

2. **Starting Point**: The cycle begins with the conversion of pyruvate (from glycolysis) into acetyl-CoA, which then combines with oxaloacetate to form citrate.

3. **Progression Through the Cycle**:
- Citrate is converted into isocitrate.
- Isocitrate undergoes decarboxylation to form alpha-ketoglutarate, releasing CO2 and reducing NAD+ to NADH.
- Alpha-ketoglutarate is further converted into succinyl-CoA, again releasing CO2 and reducing NAD+ to NADH.
- Succinyl-CoA is then converted into succinate, producing GTP (or ATP).
- Succinate is oxidized to fumarate, reducing FAD to FADH2.
- Fumarate is hydrated to form malate.
- Finally, malate is oxidized back to oxaloacetate, reducing another NAD+ to NADH.

4. **Final Product**: The last product formed in the Krebs cycle is oxaloacetate, which is a 4-carbon compound. This compound is crucial as it is regenerated to continue the cycle by combining with acetyl-CoA to form citrate.

5. **Conclusion**: Therefore, the Krebs cycle is completed with the formation of oxaloacetate (OAA), which is also known as oxaloacetic acid.

**Final Answer**: The Krebs cycle is completed with the formation of oxaloacetate (OAA).

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