Proteins are very large molecules made of amino acids. The basic structure of protein is a chain of amino acids that contain carbon, hydrogen, oxygen, and nitrogen.

The presence of nitrogen differentiates proteins from carbohydrates and fats. A difference is made between essential and nonessential proteins or amino acids. The human body requires approximately 20 different amino acids for the synthesis of its proteins. Eight of these amino acids are essential, meaning that they cannot be synthesized in the body. These are: isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Essential amino acids must be consumed from sources outside the body.

A protein is like a train with many cars linked together. Each of these cars or units is an amino acid. The many different combinations that can be formed from the 20 amino acids allow a huge number of proteins to be formed. It is just like a language where there are a few letters, but millions of words can be formed using different combinations of these letters.

For further reading, see the background file on proteins.