ABSTRACT
Proteins are linear heteropolymers of fixed chain length. A single type of protein always has the same number and composition of monomers, but different proteins have a range of monomer (amino acid) units varying from a few tens to ~1000. Twenty kinds of amino acids varying in size, shape, charge, hydrogen-bonding capacity, and chemical reactivity are commonly found in proteins. All proteins in all species are constructed from this set of 20 amino acids. They are generally self-folding, i.e., the linear chains fold into specific three-dimensional conformations that are determined by the sequence of amino acids. The three-dimensional structures of proteins are also extremely diverse, ranging from completely fibrous to globular. Interested readers may consult a number of more detailed references and books (Birkbeck College homepage: https://pps01-1.cryst.bbk.ac.uk, Chothia 1984, Doolittle 1985, Goldberg 1985, Harrison and Durbin 1985, Pauling and Corey 1951, Stryer 1988).
