Primer: amino acids and proteins

Amino acids are a family of molecules that contain an amine group (NH₂) and a carboxyl group (COOH). The ones you'll hear about the most in the context of biochemistry are alpha amino acids. An alpha amino acid has the amine group on one end, the carboxyl group on the other end, and a carbon atom between them. Attached to that middle carbon atom is the molecular structure that gives that particular amino acid its unique properties. It could be a hydrocarbon chain, an benzene ring, an alcohol. For example, the simplest alpha amino acid, glycine, has the structure H₂NCHCOOH. The possibilities are nearly endless, but we tend to focus on the twenty amino acids that are encoded in our gene sequences.

The useful thing about amino acids is that the amine group of one can react with the carboxyl group of another, forming water (H₂O) and two amino acids joined together by an amide link (...NHCO...). This can be done over and over again, with the amino acids becoming the links in a long molecular chain that can bend and coil into a unique shape. This is called a protein. Proteins provide structure, transport needed (or unneeded) materials, transmit signals, and facilitate chemical reactions in living things. Aside from water, proteins make up more of our mass than any other type of substance.

There is a small group of amino acids that we humans have to get from our diet. Since all living things utilize proteins in one way or another, we get those amino acids by breaking down the proteins of the organisms we eat. That's why you hear about needing to eat protein to stay healthy. From those "essential amino acids," our bodies can synthesize all the other amino acids we need, and we can make proteins of our own.