PROTEINS SKIN, LEATHER, AND GLUE - Archaeological Chemistry - page 323

links (or bonds ) between the amino acids within the polypeptides are
referred to as peptide bonds ] (see Fig. 70). The large number of possible
combinations of the 20 different amino acids in mammals (see Table 81)
gives rise to an extremely large number of polypeptides.
FIGURE 70 Amino acids, peptides, and proteins. The amino acids are the
building blocks of the proteins, the substances that make up the bulk of animal
cell matter. The molecules of all amino acids contain three atomic groups (a) : an
amino group, a carboxylic group, and a side (R) group. The side group is what
distinguishes each amino acid from any other. Molecules of amino acids combine
to each other, creating “peptide bonds” (b) , which are formed when an hydroxyl
ion from a carboxylic group in one amino acid and an hydrogen atom from the
amino group of another amino acid combine to form water; the water is ejected
while the CO group in one amino acid becomes attached to the amino group in
another, forming “peptides”: dipeptides, tripeptides, and polypeptides). The pro-
teins are extremely large polypeptides composed of sequences of hundreds or
thousands of amino acids (c) . The shape, properties, and hence the function of
a protein depend on the type, sequence, and number of amino acids from which
it is made up. The sequence of amino acids in a protein, which is generally
referred to as the “primary structure” of the protein, is determined by the nature
of the DNA, that is, by the genetic code of the living organism in which the
protein is made.