Each amino acid consists of a basic amino grouping and an acidic carboxyl grouping. The differentiating characteristic of amino acids is in the formation of the basic or amino group. The human body can synthesize proteins by linking amino acids link together through peptide bonds to form longer more complex molecules. Two amino acids joined together is known as a dipeptide, 3 amino acids I called a tripeptide. 4-10 amino acids linked are called oligopeptides. Multiple amino acids linked together is called a polypeptide. These molecules are complex and 3 dimensional. The structure of the protein’s side change determines its size, shape and electric charge and use in the body. Examples include the long wide protein structures like tendons, or smaller round proteins such as red blood cells. Proteins are flexible and malleable to allow them to flow through the smallest of blood vessels. Which proteins a cell makes is determined by the DNA or the cell also knows as the gene expression.