Definition of Structural biology

Structural biology is a branch of molecular biology concerned with the study of the architecture and shape of biological macromolecules—proteins and nucleic acids in particular—and what causes them to have the structures they have. This subject is of great interest to biologists, because macromolecules carry out most of the functions of a  cell, and because typically it only is by coiling into a specific three-dimensional shape that they are able to perform their functions. This shape, which is called the "tertiary structure" of a molecule, depends in a complicated way on the molecule's basic composition, or "primary structure."