What are proteins and what do they do?

Proteins are large, complex molecules that play many critical roles in the body. They do most of the work in cells and are required for the structure, function, and regulation of the body’s tissues and organs.

Proteins are made up of hundreds or thousands of smaller units called amino acids, which are attached to one another in long chains. There are 20 different types of amino acids that can be combined to make a protein. The sequence of amino acids determines each protein’s unique 3-dimensional structure and its specific function.

Proteins can be described according to their large range of functions in the body, listed in alphabetical order:

Examples of protein functions
FunctionDescriptionExample
AntibodyAntibodies bind to specific foreign particles, such as viruses and bacteria, to help protect the body.Immunoglobulin G (IgG) (illustration)
EnzymeEnzymes carry out almost all of the thousands of chemical reactions that take place in cells. They also assist with the formation of new molecules by reading the genetic information stored in DNA.Phenylalanine hydroxylase (illustration)
MessengerMessenger proteins, such as some types of hormones, transmit signals to coordinate biological processes between different cells, tissues, and organs.Growth hormone (illustration)
Structural componentThese proteins provide structure and support for cells. On a larger scale, they also allow the body to move.Actin (illustration)
Transport/storageThese proteins bind and carry atoms and small molecules within cells and throughout the body.Ferritin (illustration)