GATE 2024 BT Q.25: solution and answer

Official answer: CSource: Official answer key, GATE 2024 BT (IISc Bengaluru)

1. The TCA cycle oxidises acetyl-CoA to ${\text{CO}}_2$, producing $\text{NADH}$, ${\text{FADH}}_2$ and GTP/ATP. This is a catabolic role.

2. Its intermediates also leave the cycle as precursors for biosynthesis: oxaloacetate and $\alpha$-ketoglutarate give amino acids, succinyl-CoA gives heme, and citrate (exported to the cytosol) gives fatty acids and sterols. This is an anabolic role.

3. A pathway that works in both degradation and biosynthesis is called amphibolic, so (C) is correct.

4. (A) is wrong because the cycle is also a major oxidative route, not only a biosynthetic one.

5. (B) is wrong because it ignores the biosynthetic drain of intermediates, which anaplerotic reactions refill.

6. (D) is wrong because 'pyogenic' means pus-forming and has nothing to do with metabolism.