Peptide are short polymers of amino acids linked by peptide bonds. They have the same peptide bonds as those in proteins, but are commonly shorter in length. The shortest peptide are di-peptide, consisting of two amino acids joined by a single peptide bond. There can also be tripeptide, tetrapeptide, pentapeptide, etc. Peptide have an amino end and a carboxyl end, unless they are cyclic peptide.