Describe primary, secondary, tertiary and quaternary structure of the protein.

Primary Structure: The primary structure of a polypeptide or protein is the sequence of amino acids in the protein. In the case of insulin shown here there are two polypeptide chains in the primary structure.

Secondary Structure: Secondary structure refers to the folding of the chain of amino acids into a helix or a pleated sheet. Secondary structure arises from the geometry of the bond angle between amino acids as well as hydrogen bonds between near by amino acids.
Tertiary Structure: Tertiary structure refers to a higher level of folding in which the helices and sheets of the secondary structure fold upon themselves. This higher level folding arises for several reasons. First, different regions of the amino acid chain are hydrophilic or hydrophobic and arrange themselves accordingly in water. Second different regions of the chain bond with each other via hydrogen bonding or disulfide linkages.

Q.uaternary structure: Quaternary structure arises when polypeptide chains are bound together usually by hydrogen bonds. For example hemoglobin the oxygen carrying protein in blood has four subunits hydrogen bonded together. Most proteins with a molecular weight of 50,000 or more are made of such units.