Proteins are large, complex molecules that play many critical roles in the body. They are made up of one or more long chains of amino acid residues. There are 20 different types of amino acids that can be combined to make a protein, and the sequence of amino acids determines each proteins unique 3-dimensional structure and its specific function. Proteins perform a vast array of functions within organisms, including catalyzing biochemical reactions, providing structure and support for cells, and transmitting signals to coordinate biological processes between different cells, tissues, and organs. Some proteins are important in cell signaling, immune responses, cell adhesion, and the cell cycle. In animals, proteins are needed in the diet to provide the essential amino acids that cannot be synthesized.

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

• Antibody: Antibodies bind to specific foreign particles, such as viruses and bacteria, to help protect the body.
• Enzyme: Enzymes 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.
• Messenger: Messenger proteins, such as some types of hormones, transmit signals to coordinate biological processes between different cells, tissues, and organs.
• Structural component: These proteins provide structure and support for cells. On a larger scale, they also allow the body to move.
• Transport/storage: These proteins bind and carry atoms and small molecules within the body.

Proteins are essential for life, supplying the essential amino acids needed for the growth and maintenance of our cells.