Amino acids categories

Biopolymers are the naturally occurring macromolecular materials that are the components of all living systems. There are three principal categories of biopolymers, each of which is the topic of a separate article in the Eniyclopedia proteins (qv) nucleic acids (qv) and polysaccharides (see Carbohydrates Microbial polysaccharides). Biopolymers are formed through condensation of monomeric units ie, the corresponding monomers are amino acids (qv), nucleotides, and monosaccharides, for proteins, nucleic acids, and polysaccharides, respectively. The term biopolymers is also used to describe synthetic polymers prepared from the same or similar monomer units as are the natural molecules. 

The structures and abbreviations for the 20 amino acids commonly found in proteins are shown in Figure 4.3. All the amino acids except proline have both free a-amino and free a-carboxyl groups (Figure 4.1). There are several ways to classify the common amino acids. The most useful of these classifications is based on the polarity of the side chains. Thus, the structures shown in Figure 4.3 are grouped into the following categories (I) nonpolar or hydrophobic... 

Amino acids belong to the first category. As its name implies, an amino acid contains an amine and a carboxyl group. Amino acids join through amide linkages ... 

As mentioned in the Introduction, a variety of unusual carbohydrate -protein linkages is found in Nature. These may be placed in several categories (i) carbohydrates O-glycosylated to jff-hydroxy amino acids (ii) carbohydrates S-glycosylated to cysteine (Hi) carbohydrates N-gly-cosylated to the N-terminal amino group of the protein or (iv) in some... 

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