Proteins are made up of smaller units called amino acids. This name, amino acid, signifies that each contains an amine and an acid connected by a carbon backbone. The only structural difference between each of the 20 amino acids is the R-Group or side chain.

Amino acids are comprised of an amine, a carbon backbone, and an acid. The R-group or side-chain varies among the 20 amino acids.

There are twenty amino acids; they are all made up of the same amine-carbon-acid combination with a variable side chain. An example of the differences in the side group can be seen in the chemical structures of  methionine and alanine.

The chemical structure of alanine.

Chemical structure of methionine.

Individual amino acids are bonded together with peptide bonds (a chemical bond specific to amino acids).

Peptide bonds are formed when amino acids are joined together. Water is a by-product of this reaction.

Amino acids can also come together to form dipeptides (two amino acids), tripeptides (three amino acids), oligopeptides (3-10 amino acids), and polypeptides (10 or more amino acids). A polypeptide is a chain of amino acids as shown below.

A polypeptide chain is multiple amino acids bonded together- like dancers in a conga line.