Caption：(a) All amino acids contain an amino group (blue) and a carboxylate group (red.) Different amino acids contain different "side chains," designated here -R. (b) A dipeptide is produced when the amino group of one amino acid reacts with the carboxylate group of another to form a peptide bond (red) and one molecule of water. Notes：This dipeptide can be extended with addition of more amino acids to form the familiar biomolecule "protein" that is a polymer of amino acids.
