ABSTRACT
Amino acids consist of carbon, hydrogen, oxygen, nitrogen, and occasionally sulfur. All amino acids with the exception of proline have a terminal carboxyl group
and an unsubstituted amino (−NH2) group attached to the α-carbon. Proline has a substituted amino group and a carboxyl group. Also attached to the α-carbon is a functional group identied as R; R differs for each amino acid (Table 8.1). The general structure of amino acids can be represented as
While it is convenient to represent amino acids in this manner, in reality, amino acids exist as the dipolar ion
in the range of pH values (5.0-8.0) found within the body. In learning the structures of the essential amino acids, the student will nd it useful to remember the basic structure of alanine. All of the other amino acids have R groups that replace the terminal methyl group in alanine. For example, in valine, the methyl group is replaced with an isopropyl group; in phenylalanine, it is replaced with a phenyl group. The exception to this structure is the amino acids proline and hydroxyproline. These two are ring structures.
