structure of proteins and its type I PPT

This document discusses the different levels of protein structure: primary, secondary, tertiary, and quaternary.

1. UNIVERSITY INSTITUTE OF PHARMA SCIENCES Master of Pharmacy (Pharmacology) Principles of drug discovery (23PHT-629) 1 TOPIC OF PRESENTATION: Structure of proteins and its type Vishal bhati

2. Structure of proteins

3. Introduction Proteins are an important class of biological macromolecules which are the polymers of amino acids Proteins have different levels of organization Primary structure Secondary structure Tertiary structure Quaternary structure

4. What forces determine the structure? Primary structure - determined by covalent bonds Secondary, tertiary, - determined by weak forces Quaternary structure

5. Primary structure The primary structure of protein refers to the sequence of amino acids present in the polypeptide chain. Amino acids are covalently linked by peptide bonds or covalent bonds. Each component amino acid in a polypeptide is called a "residue” or “moiety”. By convention, the primary structure of protein starts from the amino-terminal (N) end and ends in the carboxyl-terminal (C) end

6. Secondary structure It is a local, regularly occurring structure in proteins and is mainly formed through hydrogen bonds between backbone atoms. Pauling & Corey studied the secondary structures and proposed 2 confirmations α helix β sheets

7. Alpha helix S piral structure Tightly packed, coiled polypeptide backbone core. The side chain extends outwards Stabilized by H bonding b/w carbonyl oxygen and amide hydrogen. Amino acids per turn – 3.6 Pitch is 5.4 A Alpha helical segments are found in many globular proteins like myoglobins , troponin- C, etc.

8. Beta sheet Formed when 2 or more polypeptides line up side by side. Individual polypeptide – beta strand. Each beta-strand is fully extended. They are stabilized by hydrogen bonds between N- H and carbonyl groups of adjacent chains.

9. Polypeptide chain conformations The only reasonably free movements are rotations around the C α-N bond (measured as ϕ ) and the C α-C bond (measured as Ѱ). The conformation of the backbone can therefore be described by the torsion angles (also called dihedral angles or rotation angles

10. Ramachandran plot Ramachandran plot – to visualize the backbone of amino acid residues. The amino acids with larger side chains will show less number of allowed regions within the Ramachandran plot.

11. Tertiary structure The tertiary structure defines the specific overall 3-D shape of the protein. Tertiary structure is based on various types of interactions between the side chains of the peptide chain

12. Interactions stabilizing tertiary structure Disulfide bonds Hydrophobic interactions Hydrogen bonds Ionic interactions Vander Waals force

13. Domains Polypeptide chains containing more than, 200 residues usually fold into two or more globular clusters known as domains. Fundamental functional and 3-dimensional structure of proteins. Domains often have a specific function such as the binding of a small molecule. Many domains are structurally independent units that have the characteristics of small globular proteins.

14. Quaternary structure The biological function of some molecules is determined by multiple polypeptide chains – multimeric proteins. The arrangement of polypeptide subunits is called quaternary structure. Subunits are held together by non-covalent interactions. Eg : Hemoglobin has the subunit composition a2b2