# DBT JRF 2022 — Question 45

Exam: DBT JRF 2022 · Section: B · Topic: Biochemistry › Amino Acid Properties - D & L Forms · Difficulty: Medium

## Question

Which one of the following properties of naturally occurring D-amino acids is INCORRECT:

## Options

- **A.** Peptides arising from them are more susceptible to attack by peptidases.
- **B.** They are components of bacterial cell wall.
- **C.** Peptides arising from them are not synthesized by ribosomal machinery.
- **D.** They are components of many bacterially produced peptide antibiotics.

## Answer

Option A

## Explanation

D-amino acid peptides and peptidase susceptibility: Peptidases (proteases) in biological systems are stereospecific: they evolved to recognise and cleave L-amino acid peptide bonds. Consequences for D-amino acid-containing peptides: • D-amino acid residues are NOT recognized by standard peptidases → the peptide is MORE RESISTANT to proteolytic degradation. • This is why some antimicrobial peptides (e.g., gramicidin, tyrocidine) contain D-amino acids — for stability in biological environments. • Stating they are 'more susceptible' to peptidases is INCORRECT. Application: D-amino acid incorporation is a strategy in peptide drug design to increase in vivo half-life by preventing proteolysis. Answer: The INCORRECT statement is that D-amino acid peptides are MORE SUSCEPTIBLE to peptidases (opposite is true).

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