Large, chain-like molecules, composed of amino acids, used by all organisms as chemical tools (enzymes) or as building blocks.

Amino acids are connected in proteins by peptide bonds. The sequence of the twenty possible amino acids in a given protein determines its properties. This sequence is stored and determined by the respective gene.

Folding of the amino acid chain is a particularly important feature of proteins. Common motives of folding are marked in colour in the given model of the enzyme lysozyme. Helical arrangements of the protein chain are marked in red, parallel arrangements are marked in yellow, more disordered regions are marked in white colour.