Biochem student question.

David E. Konerding dakone at uclink.berkeley.edu
Fri Oct 11 23:35:29 EST 2002


In article <85160b48.0210111046.5168712a at posting.google.com>, Saco wrote:
> "Alex Becket" <abecket at cinci.rr.com> wrote in message news:<hgsp9.63746$Cz.8026438 at twister.neo.rr.com>...
>> I am a biochemistry student at the University of Cincinnati. I am doing a
>> study of the relative hydrophobicities of amino acid side chains. My
>> question is:  does a larger surface area available to water increase or
>> decrease an amino acid's hydrophobicity? For example, tryptophan has a
>> larger surface area available to water than phenylalanine, yet phenylalanine
>> is more hydrophobic (unless using long chain alcohols as the nonpolar
>> phase).

Polarity.  A polar side chain will clearly have a much smaller
hydrophobicity than a nonpolar side chain of the same surface area.
Hydrophobicity is due to the cost of ordering waters at the surface of the
amino acid (which waters must due to minimize their interaction energy).
If you have a polar surface, the water isn't forced to order itself as
much because it can interact happily with the side chain, and thus has
a higher entropy.




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