Question

what is the distance between the 1st and 8th amino acid in an alpha helix

Answer 1

An alpha helix has 3.6 residues per turn. The pitch of the alpha-helix (the vertical distance between consecutive turns of the helix) is 5.4 Å (0.54 nm). Every main chain C=O and N-H group is hydrogen-bonded to a peptide bond 4 residues away ( O(i) to N(i+4)), also denoted by i + 4 → i hydrogen bonding. This gives a very regular, stable arrangement.

1st and 8th amino acid means there are two i + 4 → i hydrogen bondings are present. Hence the distance will be 2 x 5.4 Å = 10.8 Å

Answer: 10.8 Angstroms

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