Structural biology is a branch of
biophysics concerned with the molecular structure of biological
proteins, made up of
amino acids, and
DNA, made up of
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 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 each molecule's basic composition, or "
, the oxygen transporting protein found in red blood cells
Biomolecules are too small to see in detail even with the most advanced light
microscopes. The methods that structural biologists use to determine their structures generally involve measurements on vast numbers of identical molecules at the same time. These methods include:
Most often researchers use them to study the "
native states" of macromolecules. But variations on these methods are also used to watch nascent or
denatured molecules assume or reassume their native states. See
A third approach that structural biologists take to understanding structure is
bioinformatics to look for patterns among the diverse
sequences that give rise to particular shapes. Researchers often can deduce aspects of the structure of
integral membrane proteins based on the
membrane topology predicted by
hydrophobicity analysis. See
protein structure prediction.
In the past few years it has become possible for highly accurate physical
molecular models to complement the in silico study of biological structures. Examples of these models can be found in the
Protein Data Bank.