BIOL 301 Chapter Notes - Chapter 3.1: Alpha And Beta Carbon, Absolute Configuration, Isoleucine
4 Feb 2019
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In chemical reactions in the lab, racemic mixtures of both isomers are formed. However, in living systems, cells synthesize only l isomers of amino acids because enzymes have stereospecific active sites. At low ph, the main species in solution is the fully protonated form of the amino acid. In the first stage, the carboxyl group loses its proton. At the midpoint, there are equal concentrations of the amino acid in the -cooh and -coo- forms (the amino group is still protonated). This point represents the pka for the cooh group: there is another inflection point at a higher ph. At this point, the first proton has already been removed and the second one (from. Nh3 present as a zwitterion (the amino group is protonated and the carboxylic group is negatively charged) The amino acid is mainly: at the midpoint of this second stage, the ph is equal to the pka for the nh3.
