If a peptide was composed entirely of $\alpha$-helical structure and found to contain an integer number of complete turns, which of the following would be a possible number of amino acid residues in the peptide?
A)12
B)20
C)32
D)36
E)60

Question

Quizplus · Accepted Answer

For a complete turn of an α-helix, there are 3.6 amino acid residues. Therefore, the number of residues in an α-helix can be calculated by multiplying the number of turns by 3.6. Since the peptide is composed entirely of F1F1F1S1αF1F1F1 residues (where F represents a non-polar amino acid and S represents a polar amino acid), each repeat unit consists of 7 residues. If the peptide contains an integer number of complete turns, then the number of residues must be a multiple of 7 and the number of turns must be a divisor of the total number of residues. The only option that satisfies these criteria is D (36 amino acid residues, consisting of 10 complete turns).

If a Peptide Was Composed Entirely Of α\alphaα -Helical Structure and Found to Contain an Integer Number of and Found

If a Peptide Was Composed Entirely Of $\alpha$ -Helical Structure and Found to Contain an Integer Number of and Found