Proteins perform many functions, including storing and transporting other molecules, catalyzing metabolic processes, helping to clot blood and providing the structural framework for cells.
Amino acids are the basic building blocks that form proteins. There are 20 kinds of amino acids that make up proteins. They all have the same central structure but differ in their side chain.
The primary structure of a protein is a long chain of amino acids held together by peptide bonds. The DNA sequence of the protein's gene defines the order of the amino acids.
Small sections of a protein fold to create the protein's secondary structure. The two major types of folds are α-helices and β-sheets.
A protein's tertiary structure is its overall three-dimensional shape. This shape controls the primary function of the protein. Proteins can be divided into three main groups based on their tertiary structure: globular, fibrous and membrane proteins.
Some proteins consist of several amino acid chains combined. This level of structure is called the quaternary structure.