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BIO NMDCAT Proteins
nmdcat.online June 29, 2026

The amino acid proline is often referred to as an “α-helix breaker” because its unique cyclic structure, where the side chain is bonded to the backbone nitrogen, creates

A. A highly flexible region in the protein chain
B. A positive charge that repels other amino acids
C. A kink in the polypeptide chain and restricts the backbone rotation required for a regular α-helix
✓
D. A site for glycosylation that disrupts the secondary structure

📝 Explanation

In proline, the R-group forms a pyrrolidine ring by bonding back to the amide nitrogen. This cyclization eliminates the amide hydrogen needed for H-bonding in an α-helix and imposes a rigid, fixed kink in the polypeptide backbone, disrupting the regular helical conformation.

📖 Additional Information

  • A highly flexible region in the protein chain
  • A positive charge that repels other amino acids
  • A kink in the polypeptide chain and restricts the backbone rotation required for a regular α-helix
  • A site for glycosylation that disrupts the secondary structure

In proline, the R-group forms a pyrrolidine ring by bonding back to the amide nitrogen. This cyclization eliminates the amide hydrogen needed for H-bonding in an α-helix and imposes a rigid, fixed kink in the polypeptide backbone, disrupting the regular helical conformation.

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