Proteins serve many purposes in the body such as forming structures, providing support, defense, transporting substances, and speeding up reactions. A protein is made up of polymers called amino acids, of which there are 20 types that differ in their side groups. Amino acids are linked together through dehydration reactions to form polypeptide chains or proteins. There are a huge number of possible protein combinations due to the variety of amino acid arrangements, demonstrating life's unity and diversity. For a protein to function properly it must fold into an exact three-dimensional shape, as the protein's structure determines its role.