Proteins
These materials are building blocks of animal tissues [22, 26, 28, 31]. To a lesser extent they are also found in vegetable sources. Because the major constituents of animal bodies, including skins, hairs, and blood, are proteins, they are of much greater interest to the biochemists. Nevertheless, some proteins are important commercial materials. These include animal glues, silk, and wool. It is beyond the scope of this book, however, to render a thorough discussion of the proteins. For that reason, only some basic principles are presented here. Proteins are naturally occurring polyamides, polymer of a-amino acids. The structure can be illustrated as follows:
Because R represents many different groups, many different combinations of a-amino acids are possible and the proteins are very complex molecules. The arrangement or sequence of amino acids in proteins is referred to as their primary structure. The amide linkage is referred to in biochemistry as the peptide linkage or the peptide group. A dipeptide then is a compound consisting of two amino acids, a tripeptide of three, etc. Polypeptide refers to proteins, though the term is often reserved for lower molecular weight fractions, usually less than 10,000. Many proteins are monodisperse. This distinguishes them from many other naturally occurring polymers, such as polysaccharides, that are polydisperse.
