<span>Amino acids are
weak acids that have at least 2 pka values. They have two titratable protons
that composed of alpha carboxyl (-COOH) and alpha amino (-NH3+), but some amino
acids have a third titratable protons with ionizable groups in the R side chain.
In addition, the structure of amino
acids in peptides and proteins are determined by the charges of the titratable
group and by the R group. </span>
