Which three substances make up each of the smaller molecules that form proteins

Amino acids are the monomers that form polypeptide chains.

Amino acids consist of a carbon bonded to one hydrogen, one amino group, one carboxyl group, and one variable "R" group side chain.

1. amino group

2. carboxyl group

3. "R" group (variable)

Proteins are made from Amino acids. The composition of Amino acids all vary as there are 20 of them but the three common substance in all of them are Carbon Hydrogen and Nitrogen.