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What is a non-integral repeat in an alpha helix?

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What is a non-integral repeat in an alpha helix?

Postby qwertyqwerty » Wed Aug 15, 2012 1:46 am

What exactly is a non-integral repeat in an alpha helix and how does it arise? I was doing a question:

An a helix is a form of protein secondary structure with 3.6 residues per turn of helix. The non-integral repeat arises because it:
a) allows the formation of base pairs on the inside of the helix
b) prevents clashes between neighbouring amino acid side chains
c) positions the C=O and N-H groups to give favourable linear hydrogen bonds
d) leads to formation of an amphipathic helix
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Postby JackBean » Wed Aug 15, 2012 9:37 am

you should ask that rather on mathematical forum ;) it means the number of residues is 3.6 and not 3 or 4, i.e. there is something after the coma.
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Re: What is a non-integral repeat in an alpha helix?

Postby biorules » Wed Aug 15, 2012 11:53 pm

c) positions the C=O and N-H groups to give favourable linear hydrogen bonds
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Postby JackBean » Thu Aug 16, 2012 3:07 pm

I think b) is more important, because if it was exactly 4, then you would have all amino acids stacked one above other. Also, I think the hydrogen bonds in helix are not exactly linear.
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