2. PROTEIN
Derived from Greek word “ protos ” –
meaning primary.
It plays a variety of activities.
Each protein is a polymer of aminoacid.
Amino acids linked by a peptide bond-
polypeptide.
Each amino acid consists of a carbon atom,
an amino group, a carboxyl group as a side
chain.
3. STRUCTURE OF PROTEIN
Four levels of protein structure,
Primary structure
Secondary structure
Tertiary structure
Quaternary structure
7. PRIMARY STRUCTURE
Linear arrangement of aminoacids present in the
polypeptide chain.
Peptide bond.
Its starts amino N terminal end and ends with
carboxyl C terminal end.
Peptide bond is rigid and planer.
All peptide bond in proteins occurs in trans
configuration.
8.
9. The rotation is permitted about the bond between
nitrogen and alpha carbon atoms and between the
alpha carbon and carbonyl carbon atoms.
Two rotatory angles,
phi (φ)
Psi (ψ)
Phi and psi have a value between −180º to
+180º
10. RAMACHANDRAN PLOT
To identify secondary structure of proteins
depending upon the rotation (or) degree of
freedom of dihedral angles.
CHARACTERISTICS OF RAMACHANDRAN PLOT:
Four quadrants.
Y axis – ψ and X axis – φ .
Definite position in this plot indicate definite
secondary structure of protein.
16. SECONDARY STRUCTURE
Regular folding of primary structure is called
secondary structure.
Folding and hydrogen bonding between
neighbouring aminoacids – results to form rigid
and tubular structure called helix.
Pauling and corey identified ,
Alpha helix
Beta pleated sheet
18. ALPHA - HELIX
Coiled structure.
Peptide bond would form a right handed helical
structure by simple twist about the α-carbon-to-
nitrogen and the α-carbon-to-carboxyl carbon
bonds.
It can be right handed (or) left handed.
Stabilized by hydrogen bonded to the NH and CO
group of main chain.
19. Pitch of 5.4 Å .
Per turn of helix 3.6 aminoacids are present.
One residue occupies 1.5 Å.
Conformations with φ = − 60º and ψ = − 45º to −
50º.
Alpha helix found in protein alpha keratin.
20. BETA PLEATED SHEET
Pauling and corey identified a stable conformation
– Beta pleated sheet.
Stabilized by hydrogen bond between NH and CO
groups in different polypeptide strands.
One residue occupies 3.5 Å.
Two types,
Parallel β pleated sheet
Antiparallel β pleated sheet
21. Parallel beta pleated sheet:
The polypeptide strands run in the same direction.
N-C terminus.
22. Antiparallel beta pleated sheet:
The polypeptide strands run in the opposite direction.
The N- is opposite to the C terminus.
23. Both parallel and antiparallel beta sheets have
similar structure.
Random coil:
It is the third type of secondary structure.
26. TERTIARY STRUCTURE
The tertiary structure of protein is the overall
three Dimensional shape that arises from all of the
secondary structures of its polypeptide chain.
functions are depends…
Globular (or) fibrous tertiary structure.
Do not occur randomly.
27. Forces involved in stabilizing tertiary structure,
including
Electrostatic forces
Vander Waals
Hydrogen bond
Disulfide bonds
For example,
Myoglobin
28. Myoglobin
Relatively small.
Compact macromolecule.
Oxygen binding hemi protein.
Found in muscle cells.
Molecules contain single polypeptide
chain of 153 aminoacid residues.
31. QUATERNARY STRUCTURE
Connectivity between two (or) more polypeptide
chain.
Complexity – very high
Some globular proteins consists of two (or) more
interacting peptide chains.
These chains may be identical (or) different in
primary structure.
32. Forces are involved,
Disulfide
Hydrogen
Hydrophobic
Ionic bonds
Example,
Hemoglobin