biochem help

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musiclink213

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I need help with biochem. i have an exam tomorrow, and i'm having a problem with calculating the lengths of polypeptides. so here's question 1.

Calculate the length in nanometers of a polypeptide chain containing 105 a.a. recidues if a) it exists entirely in alpha helical form, or b) if the backbone bonds are fully extended and linear.

question 2:
The polypeptide chain of a given protein is alpha-helical in some segments and has the beta conformation in others. The protein has a MW of 240,000 and a contour length of 506 nm. Calculate the fraction of the molecule that exists in the alpha helical configuration.

i think i'm ok with everything else, but for some reason, how to calculate the lengths appears to elude me.

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hey,

each aa is 1.5 angstroms in an alpha helix, so 105 residues X 1.5 angstroms, and u have your length for that helix. If it was straight, then it would be 3.5 angstroms per residue (assuming the chain was part of a parallel beta sheet; i dont flat out know the true length if it was stretched out but u could find that out in a book somewhere).
 
It's in your book somewhere, like the above poster said. I tried to forget stuff like that as soon as I could.
 
The pitch of the alpha helix is 0.54nm, isn't it? and at 3.6 residues/turn, then it's 105 aa*0.54nm/3.6 aa.
The straight chain... that's just a straight multiplication. Numbers should be in the book.
 
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