Amino Acids
Amino acid is a monomer.
chain of amino acids form polypeptides/dipeptides

Different amino acid have different R groups attached to them. The amino acid carboxyl group stays the same.
here are 20 amino acids naturally incorporated proteins:
Valine, Leucine, Alanine, Arginine, Proline, Cysteine, Threonine, Methionine, Histidine,
Glutamine, Lysine, Aspartic acid, Glutamic Acid, Serine, Phenylalanine, Tyrosine, Tryptophan, Asparagine, Glycine,
There are 8 amino acids which must be consumed through foods:
Histidine, Lysine, BCAAS (Branched Chain amino acid), Phenylalanine, Methionine
Dipeptides are formed by 2 amino acids in a condensation reactions.