Return to Contents Chapter 27: Amino Acids, Peptides and Proteins Ch 27 contents
Amino Acid Stereochemistry Fischer projections are commonly used to represent amino acids. Recall that Fischer projections are typically drawn with the longest chain oriented vertically and with the more highly oxidised C at the top.

For the 20 α-amino acids that occur naturally in proteins, if we focus on the α-center, a chirality center, and draw the Fischer projection putting the -CO2H group up, then the ammonium group, NH3+, will be on the left, making it like L-glyceraldehyde where the -OH is on the left (review ?).
Hence,  we have the L-amino acids.  You can check this out using the 3D-JMOL images given below:

 
Fischer diagram of R-(+)-glyceraldehyderevealing the stereochemistry of the Fischer diagram
 
alanine
tryptophan
S-(-)-glyceraldehyde
or
L-glyceraldehyde
QUESTIONS NOTE : Although only the L-amino acid series are incorporated into natural proteins, the D-amino acids also occur naturally.
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© Dr. Ian Hunt, Department of Chemistry, University of Calgary