Protein

macromolecules consisting of long sequences of &alpha;-amino acids [H2N–CHR–COOH] in peptide (amide) linkage (i.e. under elimination of H2O between the &alpha;-NH2 and &alpha;-COOH moieties of successive residues)

Description
Protein is three-fourths of the dry weight of most cell matter and is involved in structures, hormones, enzymes, muscle contraction, immunological response, and essential life functions. The amino acids involved are generally the 20 &alpha;-amino acids (glycine, L-alanine, etc.) recognized by the genetic code. Cross-links yielding globular forms of protein are often effected through the –SH groups of two sulfur-containing L-cysteinyl residues, as well as by non-covalent forces (hydrogen bonds, lipophilic attractions, etc.)