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
1. Primary structure
2. Secondary structure
3. Tertiary structure
4. 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
o α helix
o β sheets

7. Alpha helix
• Spiral 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
i. Disulfide bonds
ii. Hydrophobic interactions
iii.Hydrogen bonds
iv.Ionic interactions
v. 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