Protein structure and variety

Proteins are composed of chains of amino acids. A typical protein is about 400 amino acids long. As there are 20 different types of naturally occurring amino acids, many different proteins can be made. Different proteins are made of different combinations of amino acids.

The sequence of amino acids in the chain determines how the chain will fold up to make the protein, so different proteins have different three-dimensional shapes.

The three-dimensional shape of a protein determines its function. This is because proteins form attachments and interact with many other molecules and structures inside organisms.

The shape of a protein determines what it can interact with, just like the shape of a key determines which locks it can operate.

A straight amino acid sequence folds into a precise 3D shape, the protein functions as an enzyme.

Functions of proteins

Most of the proteins in your body can be grouped into four categories based on the function they carry out.

CategoryFunctionExamples
StructuralForms supporting frameworks inside cells and forms body structuresTubulin: forms spindle fibres during mitosis and Keratin: the protein that makes up hair and nails
EnzymesCatalyse biological reactionsATPase: catalyses the breakdown of ATP and Cellulose synthase: catalyses the formation of cellulose from glucose molecules
HormonesCommunication between different parts of the body. Hormones are released from endocrine glands and are transported in the blood to target cells Insulin: released from pancreas, stimulates liver cells to take up glucose from the blood and Glucagon: released from pancreas, stimulates liver cells to release glucose into the blood
AntibodiesPart of the immune system. They are produced by white blood cells and can bind to specific bacteria and viruses to label them for destruction by other types of white blood cells Your body produces around one million different types of antibody