Which of the following steps of respiration is amphibolic ?

Options

A. Glycolysis
B. Oxidative decarboxylation of pyruvate
C. TCA cycle
D. Oxidative phosphorylation

Answer

To determine which step of respiration is amphibolic, we need to analyze the options provided and understand the definitions of anabolic and catabolic pathways.

### Step-by-Step Solution:

1. **Understanding Amphibolic Pathways**:
- Amphibolic pathways are those that involve both anabolic (building up) and catabolic (breaking down) processes.

2. **Analyzing the Options**:
- **Glycolysis**: This process is primarily catabolic as it breaks down glucose into pyruvate, releasing energy.
- **Oxidative Decarboxylation of Pyruvate**: This step is also primarily catabolic, as it converts pyruvate into acetyl-CoA, releasing CO2 and generating NADH.
- **TCA Cycle (Krebs Cycle)**: This cycle is known to be amphibolic because it involves both the breakdown of acetyl-CoA to produce energy (catabolic) and the generation of intermediates that can be used for biosynthesis (anabolic).
- **Glyoxylate Cycle**: This cycle is primarily anabolic, as it is involved in the conversion of fatty acids into carbohydrates.
- **Oxidative Phosphorylation**: This process is purely catabolic as it involves the production of ATP through the breakdown of NADH and FADH2.

3. **Conclusion**:
- The TCA cycle is the only option that exhibits both anabolic and catabolic characteristics. Therefore, the correct answer is the TCA cycle.

### Final Answer:
The amphibolic step of respiration is the **TCA cycle** (Krebs cycle).