Proteins are macro-molecule made up of many polypeptide chains joined together by peptide bonds. They have four structures; primary, secondary, tertiary and quaternary and can be divided into globular proteins, fibrous proteins and membrane proteins.
The primary structure of proteins give the linear sequence of the amino acids and thus the types. All protein posses this structure. In the secondary structure folding is introduced of which there are two types; alpha-helix and beta-pleated sheets. Next is the tertiary structure which ha one polypeptide chain while the quaternary as more than one. The tertiary structure represents the 3-dimensional shape of the protein in space and it is held together by electrostatic forces, hydrogen bonds, sometimes covalent bonds like disulphide bond and most importantly hydrophobic interactions. These bonds are also present in the quaternary structure of proteins.
However these bonds can be broken or disrupted by denaturation. Some examples of substances that denature proteins are heat, chemicals such as chaotropes and detergents, strong acids or bases, ultra violet radiation and metal ions. Nevertheless denaturation can be reversed in some instances by dialysis.