Protein

Proteins are chains of amino acids folded into precise three-dimensional shapes; the shape determines what the protein binds and what it does. Genes encode proteins, so a mutation in a gene can change the protein's shape and behaviour, for example locking a kinase permanently 'on'. Drugs are designed to fit into a pocket on a target protein and block or alter its function, and antibodies recognise proteins on the cell surface; immunohistochemistry stains a protein in tissue to see how much of it a tumour makes.