Glossary · Sinh học
Protein
A large, complex molecule with many roles in the body. A protein is one or more long, folded chains of amino acids — each chain called a polypeptide — and that amino-acid sequence is determined by the DNA sequence of the protein-encoding gene.
Proteins are one of the most abundant organic molecules in living systems and have the most diverse range of functions of all macromolecules. They act as the enzymes that catalyse the chemical reactions life needs, serve as contractile proteins such as actin and myosin that effect muscle contraction, and are required for the structure, function and regulation of the body's tissues and organs.
The building block is the amino acid. Each amino acid shares the same fundamental structure: a central carbon atom bonded to an amino group, a carboxyl group and a hydrogen atom.
A protein's function comes from its shape, and shape has four levels: the sequence of amino acids in the polypeptide chain is its primary structure; the local folding of the polypeptide in some regions gives the secondary structure, most commonly the α-helix and β-pleated sheet; the polypeptide's unique three-dimensional structure is its tertiary structure; and where a protein forms from several polypeptides, or subunits, the interaction of those subunits forms the quaternary structure.