BiomoleculeshardNUMERICAL

In the -helix secondary structure of a protein, the critical intramolecular hydrogen bonding betweenBiomolecules Chemistry Question

Question

In the $\alpha$ -helix secondary structure of a protein, the critical intramolecular hydrogen bonding between the $>C=O$ group of one residue and the $-NH$ group of the fourth residue creates a closed structural loop. Exactly how many atoms constitute this specific repeating hydrogen-bonded chelate ring?

Answer: 13

💡 Solution & Explanation

The standard $\alpha$ -helix configuration is stabilized by intramolecular hydrogen bonds connecting the carbonyl oxygen of amino acid residue $(i)$ with the amide hydrogen of residue $(i+4)$. Tracing the backbone path through these bonded atoms yields a continuous $13$ -membered chelate ring.

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