Free-form amino acids do not contain peptide bonds as they are the monomer building blocks of proteins. As explained by Dr. John W. Kimball, peptide bonds form between two amino acids, creating long polypeptide chains. Proteins are composed of one or more of these polypeptide chains.
Twenty different amino acids are used to synthesize proteins. Amino acids consist of a central alpha carbon atom, hydrogen atom, carboxyl group, amino group and a functional group that determines the type of amino acid. Kimball explains that during protein synthesis, a covalently linked peptide bond is formed between the carboxyl group of one amino acid and the amino group of the next sequential amino acid.