Replies:
First, what they have in common is the basic structure HXN-CHR-CO2H. The
differences are the substituent groups N and R. For most of the twenty
common biological amino acids, X = Hydrogen. The R groups are what set them
apart. In one of the common biological amino acids, proline, the R group
curls around and connects to the N atom, so the substituent "X" is the end
of the R group.
Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois
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