The smaller unit molecules which combine to form proteins and polypeptides are called amino acids.

Here's a breakdown:

* Proteins are large, complex molecules made up of one or more long chains of amino acids.

* Polypeptides are chains of amino acids that are shorter than proteins.

* Amino acids are the building blocks of proteins. They have a central carbon atom bonded to an amino group (NH2), a carboxyl group (COOH), a hydrogen atom (H), and a side chain (R group) that varies between different amino acids.

The sequence of amino acids in a protein or polypeptide determines its three-dimensional structure and its function.