1.TERTIARY STRUCTURE OF PROTEINSTertiary Structure describes the shapes which form when the secondary spirals of the protein chain further fold up on themselves.The overall three-dimensional arrangement of all atoms in a protein.

2. DOMAINS are the fundamental functional and three dimensional structural units of a polypeptide.Polypeptide chains that are greater than 200 aminoacids in length consists of two or more domains.The core of the domain is built from super secondary elements(motifs) 3. Folding of the peptide chain within a domain usually occurs independentlay of folding in others domain.Therefore each domain has a characteristics of a small compact globular protein that is structurally independent of the other domains in the polypeptide chain. 4. Interactions stablizing tertiary structureThe unique three dimensional structure of each polypeptide is determined by the aminoacid sequence.Interactions between the side chains of aminoacids guide the folding of the polypeptide to form the compact structure .Four types of interactions cooperate in stablizing the tertiary structure of globular proteins. 5. Disulfide bondHydrophobic interactionsHydrogen bondsIonic interactions 6. QUATERNARY STRUCTURE Some proteins contain two or more separate polypeptide chains or subunits.The arrangement of these protein subunits in three-dimensional complexes constitutes quaternary structure.For example globin of hemoglobin is made up of four subunit,Enzyme pyruvate dehydrogenase is madeup of three subunits 7. Protein undergo assisted foldingA specialized group of proteins, named chaperones are required for the proper folding of many species of proteins.Molecular chaperones: Hsp 70, Hsp 40, Dna K, Dna J, Grp E, chaperoninsetc.Protein disulfide isomerase (PDI): catalyzes the interchange or shuffling of disulfide bonds.Peptide prolyl cis-trans isomerase (PPI): catalyzes the interconversion of the cis and trans isomers of proline peptide bonds. 8. Protein misfoldingProtein folding is a complex,trial and error processthat can some times result in improperly foldedmolecules.Deposits of misfolded proteins are associated with anumber of diseases including1.Amyloidoses2.Prion disease