An amino acid peptide is a molecule that contains a short chain of amino acids joined together by peptide bonds. These molecules have the same basic structure as proteins, but there is one specific difference between them. The characteristic that differentiates a protein from an amino acid peptide is the number of amino acids that are joined together to make up the molecule. Generally, if there are less than 50 amino acids in the chain, then it is considered to be an amino acid peptide.
Within both amino acid peptides and proteins, peptide bonds hold the amino acids together. Peptide bonds are an example of covalent bonds, which are formed when electrons are shared between two different atoms. In the case of amino acids, the bond forms between the carboxyl group (-COOH) of one amino acid and the amino group (-NH2) of another. During the reaction that links the two amino acid molecules together, a molecule of water (H2O) is released when a hydrogen ion (H) from the amino group joins with a hydroxyl (OH) from the carboxyl group.
The shortest amino acid peptide that can be formed is called a dipeptide because it contains only two amino acids. From there, they increase in length up to about 50 amino acids. As more amino acids are joined together, tri-, tetra- and pentapeptides are formed. These molecules are also referred to as polypeptides, which means "many peptides." To form proteins, at least two polypeptides must be joined together.
Amino acid peptides and proteins have many different roles with the cells of animals. Both can form hormones and enzymes, which regulate the functioning of certain cells and can stimulate or inhibit particular reactions within cells. They also play a role in the support of different parts of the animal body as they are integral in many different types of cells and tissue, including hair, nails, muscle, bone and skin cells.
The sequence of the amino acid peptide is determined by the DNA of the organism. The long strands of nucleic acids provide the code for which amino acids should be attached to which. Initially, DNA is transcribed into RNA, which is then translated into an amino acid peptide or protein. A combination of three DNA nucleic acids, or a codon, corresponds to each amino acid. There are 20 different amino acids that can be joined together to form an amino acid peptide chain.