# DBT JRF 2022 — Question 34

Exam: DBT JRF 2022 · Section: A · Topic: Biochemistry › Carbon & Nitrogen Metabolism · Difficulty: Medium

## Question

The enzyme that links carbon and nitrogen metabolism is:

## Options

- **A.** Glutamine synthetase.
- **B.** Transketolase.
- **C.** Glutamate dehydrogenase.
- **D.** Enolase.

## Answer

Option A

## Explanation

Glutamine synthetase links carbon and nitrogen metabolism: $\text{Glutamate} + \text{NH}_4^+ + \text{ATP} \xrightarrow{\text{Glutamine synthetase}} \text{Glutamine} + \text{ADP} + P_i$ This reaction is critical because: • It incorporates inorganic ammonium ( $\text{NH}_4^+$ ) — the primary form of inorganic nitrogen — into glutamine (an organic nitrogen compound). • Glutamine then serves as a nitrogen donor for nucleotide synthesis, amino acid transamination, and many other biosynthetic reactions. • It thus connects carbon skeletons (from carbon metabolism) with nitrogen assimilation. Other options: • Transketolase: transfers 2-carbon units in pentose phosphate pathway (carbon metabolism only). • Glutamate dehydrogenase: catalyses glutamate ⇌ α-ketoglutarate + NH₃ (also involved but less 'primary'). • Enolase: glycolytic enzyme (carbon metabolism only). Answer: Glutamine synthetase (Option 1).

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