Important Question About AMINO ACIDS ?????

[Shaun D. Black]

ybou at fox.nstn.ns.ca (Yvon Boudreau) on 13 Sep 1994 writes:
> 
> 1.) Why are the amino acids of the "alpha" type?
> 2.) Why are they of the "levo" type?
> 
> 	 These questions were given to me in my grade 12 biology class.
>  Help would be very much appreciated!
> 
My reading of the scientific literature suggests that noone really knows the
answer to these questions.  Probably the most important thing for a grade
12 biology class to know is that these observations are nearly inviolate
throughout all known organisms/proteins in nature.

A guess/hypothesis concerning (1) is that beta, gamma, etc. amino acids would
impart too much backbone flexibility and thus degrees of freedom to a folding
polypeptide chain.  In all likelihood non-alpha amino acids in peptide
linkage would not fold.  As for (2), this has been covered in an extensive
thread on Methods-and-Reagents a few months back; check the archives,
preferably by a Gopher search.  Briefly, polypeptides of L-amino acids form
structures with right-handed helices, right-handed twists to beta strands,
left-handed twist to beta sheets, etc.  Polypeptides of D-amino acids form
the same structures but of the _opposite_ handedness.  I hope this helps you
a bit.  Best regards,  
  =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= 
  = Shaun D. Black, PhD   | Internet address:     shaun at jason.uthct.edu = 
  = Dept. of Biochemistry | University of Texas Health Center, at Tyler = 
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