Protein

biology

Definition

Protein

A protein is a large biomolecule composed of one or more chains of amino acids joined by peptide bonds. The sequence of amino acids determines the chain’s fold, and the fold determines the protein’s function.

Formally, a protein is a function over an alphabet of 20 residues. Let the chain be the sequence $s=(a_1,a_2,\dots ,a_n)$ with each $a_i\in \mathcal{A}$, where $\mathcal{A}$ is the 20-letter amino-acid alphabet. The protein’s structure and function are determined by the map

$$F:{\mathcal{A}}^n\to \mathcal{S},s\mapsto F(s),$$

where $\mathcal{S}$ is the space of folded three-dimensional structures.