PROTEINS SKIN, LEATHER, AND GLUE - Archaeological Chemistry - page 325

which control the activity of cells or organs, and the antibodies , which
protect the body from foreign particles and organisms. The information
for making specific proteins is determined by the nature of the DNA of a
living organism. The proteins can be conveniently classified by either their
function or their shape. In Table 82 are classified some common proteins
by their function in living organisms.

TABLE 82 Some Common Proteins

Protein Natural function Human uses

Structural Proteins

Collagen, myosin Make up muscles, skin, and part of the Food

animal skeleton

Keratin Makes up hair, wool, nails, and feathers Making yarn

Fibroin Makes up silk Making yarn

Motorial Proteins
Myosin, actin Contract and change shape Food

Storage Proteins

Seed storage Store nutrients until germination Food

Hemoglobin Stores oxygen Adhesive, food

Egg albumin Stores nutrients Adhesive, food

Milk casein Stores nutrients Adhesive

Regulatory Proteins
Hormones Regulate metabolic processes

Enzymes Regulate catalytic activity

Defensive Proteins

Snake venom Provide body protection

When classified by shape, two main different types of proteins can be
distinguished: fibrous and globular proteins . Myosin , the protein that
makes up the muscles, keratin , which makes up the nails and hairs, and
collagen , in the bones, tendons, and skin of mammals, are all fibrous pro-
teins . They are insoluble in water and are mostly tangled around each
other and stretched out (see Fig. 71). In the globular proteins the polypep-
tide chains are folded into the shape of balls - as, for example, in the
hemoglobin of blood, which transports oxygen to the various parts of the
body, or the albumin of eggs. A moderate increase in temperature can
provide enough energy not only to unfold the polypeptide chains but also