# DBT JRF 2022 — Question 3

Exam: DBT JRF 2022 · Section: B · Topic: Biochemistry › Peptide Molecular Weight Calculations · Difficulty: Medium

## Question

What will be the molecular weight of the tri-peptide Trp-Gly-His? Molecular weights of Trp, Gly, and His are 204.2, 75.07, and 155.2 respectively.

## Options

- **A.** 434.47
- **B.** 300.00
- **C.** 398.47
- **D.** 502.25

## Answer

Option C

## Explanation

Molecular weight of tripeptide Trp-Gly-His: Individual amino acid molecular weights: • Trp (Tryptophan) = 204.2 Da • Gly (Glycine) = 75.07 Da • His (Histidine) = 155.2 Da When two amino acids join via a peptide bond, one water molecule (18 Da) is lost per bond: $\text{MW}_{\text{tripeptide}} = \sum \text{MW}_{\text{aa}} - (n-1) \times 18$ where $n = 3$ amino acids, so 2 peptide bonds form: $= 204.2 + 75.07 + 155.2 - 2 \times 18 = 434.47 - 36 = 398.47\,\text{Da}$ Answer: 398.47 Da (Option 3).

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