Question

A newly identified viral protein contains one long α-helix spanning 60 amino acid residues. The number of main chain H-bonds formed in this helix is _______. (Answer in integer)

Hint:

When calculating hydrogen bonds in an α-helix, remember that the bonds start forming from the fifth residue to allow for the 3.6 residues per turn characteristic of the α-helix structure.

Answer 1

In an α-helix, the hydrogen bonds are typically formed between the carbonyl oxygen of one amino acid residue and the amide hydrogen of another amino acid residue that is four residues earlier in the sequence. This creates a stabilizing network along the helix.
Counting Hydrogen Bonds: Given that the helix spans 60 amino acids, the first hydrogen bond can form between the carbonyl oxygen of the first residue and the amide hydrogen of the fifth residue. This pattern continues until the end of the helix. 
Calculation: Since each subsequent hydrogen bond involves an amino acid four residues down the chain, the total number of hydrogen bonds formed will be: [ 60 - 4 = 56 ] Thus, there are 56 hydrogen bonds in a 60-residue long α-helix. Conclusion:
This calculation accounts for the hydrogen bonds starting from the first possible bond in a contiguous α-helix and does not count any possible terminal disruptions or variations in structure at the ends of the helix.