Some Familiar Proteins

The hair on your head is an example of an almost pure protein. So is silk. The protein of hair is called keratin by chemists, and the protein of silk is called fibroin.

Both keratin and fibroin are comparatively simple proteins. Their molecules consist of amino acids strung together in more or less a long straight line. Such lines of amino acids are called polypeptides.

In the 1940’s chemists learned to manufacture quite long polypeptide chains in the laboratory. They used only one or two different amino acids in doing so, however.

Then, in the 1950’s, chemists learned how to put together amino acids of many different varieties, one by one, just in a particular order. By 1960, a protein built up of 23 amino acids, was manufactured in the laboratory. It was found to behave just like a similar small mole­cule formed by the body. However, 23 amino acids are a long way from the hundreds and thousands of amino acids found in the larger proteins made by the body.

Still, fibroin isn’t much more complex than these laboratory crea­tions. Its molecule contrasts of over 250 amino acids of 14 different kinds. Eighty-five per cent of the molecule is made up of only three different amino acids, and those three happen to be the simplest of all. It is for this reason¹ that silk doesn't play a vital role in life. It is just used by the silkworm² to make a soft cocoon for itself.

Protein such as fibroin and keratin are called fibrous proteins. In general, fibrous proteins are strong, sturdy (крепкий) and tough (прочный). Keratin, for instance, is the chief protein not only of hair, but of skin, nails (ногти), hooves (копыта), scales (чешуя), horns (pora) and feathers (перья). Another important fibrous protein is collagen, which occurs in cartilage (xpящ), ligaments (связки) and tendons (cyxoжилия).

The really important proteins, however, are the globular proteins. In these, the polypeptide chains are not merely straight lines, but existing complicated loops (петля) and twists (изгиб) which are never quite the same in any two different proteins.

Notes

1. it is for this reason – именно по этой причине

2. silkworm – шелковичный червь