Why are proteins considered to be heteropolymers?

A polymer is a giant molecule made up of many smaller molecules called

monomers. If all the monomers are identical the polymer is a homopolymer.

For example starch is made solely of glucose molecules so starch is a homopolymer. If the monomers are not identical the polymer is heteropolymer . Proteins are made up of up to 20 different amino acids, so proteins are heteropolymers.