The order in which the amino-acids are placed within the polypeptide determines the tertiary structure and therefore the function of the given protein. Amino acids have different functional groups like methyl(CH3), phenyl(C6H5). Those functional groups can interact with molecules like glucose determining reactions, the proteins that catalyze reactions are called enzymes. Other functional groups of amino acids can be the sulfate groups. For example, insulin has 2 polypeptide chains(Chain A has 21 amino acids, and chain B, 30). Between the two polypeptide chains, 2 disulfide bonds form altering its shape.
