Arginine is the last product of the urea cycle from which urea is clipped for excretion. His is the precursor molecule to hidtamine, the compound that causes many allergic reactions and which may be blocked by the use of anti-histamines. Histamine synthesis may be stimulated by the influence of norepinephrine or psychological stress. The essential amino acids are phe, val, trp, thr, ile, met, lys, leu. The semi-essential amino acids are his and arg.
Amino acids are the building blocks of proteins.
Figure 5 and Figure 6 . The peptide bond is unique in that it appears to be a single bond, but has the characteristic of a double bond, i.e., it is a rigid bond. This kind of bond only occurs between amino acids. As the amino acid chain increases, the next amino acid adds onto the previous carboxyl group by its amino group, Figure 7 . The farthest amino acid residue to the right is the amino acid in the protein that has the highest number and, as a general rule, is the free carboxyl end or the C-terminus.