# DBT JRF 2020 — Question 23

Exam: DBT JRF 2020 · Section: A · Topic: Biochemistry · Difficulty: Easy

## Question

Trypsin cleaves a protein at the

## Options

- **A.** C-terminus side of Val/Ile residues
- **B.** C-terminus side of Arg/Lys residues
- **C.** N-terminus side of Val/Ile residues
- **D.** N-terminus side of Arg/Lys residues

## Answer

Option B

## Explanation

Trypsin is a serine protease of the digestive system (secreted as trypsinogen from the pancreas, activated by enteropeptidase in the duodenum). It cleaves peptide bonds on the CARBOXYL (C-terminal) side of the basic amino acid residues arginine (Arg, R) and lysine (Lys, K), EXCEPT when followed by proline. The catalytic triad (Ser195, His57, Asp102) acts as a charge relay to hydrolyse the amide bond. Trypsin is widely used in proteomics for peptide mass fingerprinting in mass spectrometry because it produces predictable, well-ionised peptide fragments.

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