Structural biology is a branch of
molecular biology,
biochemistry, and
biophysics concerned with the molecular structure of biological
macromolecules, especially
proteins and
nucleic acids, how they acquire the structures they have, and how alterations in their structures affect their function. This subject is of great interest to biologists because macromolecules carry out most of the functions of
cells, and because it is only by coiling into specific three-dimensional shapes that they are able to perform these functions. This architecture, the "
tertiary structure" of molecules, depends in a complicated way on the molecules' basic composition, or "
primary structures."