Amino acids 1

Like carbohydrates and lipids, proteins contain carbon, hydrogen and oxygen.
Proteins also contain nitrogen.

The basic units that make up proteins are amino acids
The formula for an amino acid is shown below:

In the diagram R represents a side chain.
There are 20 different naturally occuring side chains, so there are 20 different amino acids. The different side chains will have different properties - some are acidic, some can form hydrogen bonds, some contain sulfur, some are hydrophobic and some hydrophylic - so the 20 amino acids will have different chemical properties.