Since each of these groups can be either protonated or deprotonated, the structure of an amino acid depends on the pH of the solution it is in. Asp, Glu Amino acids can be joined together through condensation or dehydration reactions between the carboxyl group of one amino acid and the amino group of the next. The result is a new bond between the carboxyl carbon and the amino nitrogen. This bond is called a peptide bond . Two amino acids joined together in this manner are referred to as a dipeptide .
Similar principles apply to peptides consisting of more than two amino acids.
Three amino acids make a tripeptide, four make a tetrapeptide, five make a pentapeptide, and so on. When several amino acids are joined, the resulting structure is referred to as an oligopeptide, and when thousands are joined, it is called a polypeptide , or protein . Proteins are extremely important to the body, acting as structural components, enzymes, hormones, and more. Thus, extreme diversity is required for proteins. This diversity comes from the fact that there are 20 different amino acids found commonly in living things.