3. The term "protein" originates from the Greek word 'Proteios'
meaning holding the first place, as proposed by Berzelius, a
Swedish chemist.
Proteins are the predominant organic molecules in living
organisms.
They are present in all parts of the cell and make up
approximately 50% of the cellular dry weight.
play a crucial role in the structure and function of life.
About 3/4th of the total dry body weight is comprised of
proteins.
INTRODUCTION
4. Proteins are intricate organic molecules with molecular weights
varying from 6000 to several million.
They consist of carbon, hydrogen, oxygen, nitrogen, and
occasionally phosphorus and sulfur.
Amino acids are the building blocks of proteins, linked together
by peptide bonds.
The properties and actions of proteins are determined by the
specific amino acids they contain.
Composition
5. Proteins contain carbon, hydrogen, oxygen, nitrogen, and small
amounts of sulfur.
Composed of amino acids linked together by peptide bonds.
Act as catalysts, enzymes that speed up chemical reactions.
Provide structural support for cells.
Transport substances across cell membranes.
Act as a defense mechanism against pathogens (antibodies).
Respond to chemical stimuli.
Secrete hormones.
Physical Properties
6. Proteins are essential biological macromolecules composed of
amino acid polymers.
Biochemists have identified
distinct levels of structural
organization for proteins.
The levels of protein
structure include:
1. Primary structure
2. Secondary structure
3. Tertiary structure
4. Quaternary structure
STRUCTURE OF PROTIEN
7. The primary structure of a protein is determined by the specific
sequence of amino acids in the polypeptide chain.
Amino acids are connected through peptide bonds to form the
polypeptide chain.
Each individual amino acid in a polypeptide chain is referred to
as a "residue" or "moiety".
Conventionally, the primary structure of a protein is described
starting from the amino-terminal (N) end and ending at the
carboxyl-terminal (C) end.
PRIMARY STRUCTURE
8. IMPORTANCE OF PRIMARY STRUCTURE
• To predict 20 and 30 structures from sequence
homologies with related proteins. (Structure
prediction)
• Many genetic diseases result from abnormal amino acid
sequences.
• To understand the molecular mechanism of action of proteins.
• To trace evolutionary paths.
METHODS OFAMINOACID SEQUENCE DETERMINATION
• End group analysis – Edman degradation.
• Gene sequencing method.
IMPORTANCE OF PRIMARY
STRUCTURE
9. SECONDARY STRUCTURE
• Localized arrangement of adjacent amino acids formed as the polypeptide
chain folds.
• It consists of
• Linus Pauling proposed some essential features of peptide units and
polypeptide backbone. They are:
– The amide group is rigid and planar as a result of resonance. So rotation
about C-N bond is not feasible.
– Rotation can take place only about N- Cα and Cα – C bonds.
– Trans configuration is more stable than cis for R grps at Cα
• From these conclusions Pauling postulated 2 ordered structures α helix and
β sheet
α-helix
β-pleated sheet
β-bends
Non repetitive structures
Super secondary structures
SECONDARY STRUCTURE
10. Spiral structure
Tightly packed, coiled
polypeptide backbone core.
Side chain extend outwards
Stabilized by H bonding
b/w carbonyl oxygen and
amide hydrogen.
Amino acids per turn – 3.6
Pitch is 5.4A
Alpha helical segments are found
in many globular proteins like
myoglobins, troponin- C etc.
ALPHA HELIX
H bonding
11. BETA PLEATED SHEET
Formed when 2 or more polypeptides
line up side by side.
Individual polypeptide - β strand
Each β strand is fully extended.
They are stabilized by H bond b/w
N-H
and carbonyl grps of adjacent chains.
2 types
Parallel Anti -Parallel
N
N
C
C
C
N
N
C
12. TERTIARY STRUCTURE
Tertiary structure is the three-
dimensional conformation of a
polypeptide.
The common features of protein
tertiary structure reveal much about
the biological functions of the proteins
and their evolutionary origins.
The function of a protein depends on
its tertiary structure. If this is
disrupted, it loses its activity.
13. INTERACTIONS STABILIZING 30
STRUCTURE
• This final shape is
determined by a variety of
bonding interactions
between the "side chains"
on the amino acids.
• Hydrogen bonds
• Ionic Bonds
• Disulphide Bridges
• Hydrophobic Interactions:
14. • The biological function of some
molecules is determined by
multiple
polypeptide chains –
multimeric proteins.
• Arrangement of polypeptide sub
unit is called quaternary
structure.
• Sub units are held together by
non covalent interactions.
• Eg: Hemoglobin has the
subunit composition a2b2
QUATERNARY STRUCTURE
Quaternary structure of hemoglobin.
15. CONCLUSION
• Proteins are extraordinarily complex molecules. Of all the
molecules encountered in living organisms, proteins have the
most diverse functions.
• So a basic understanding of the structure of proteins is
necessary to comprehend its role in organisms.
• Further researches will provide more insight into the structure
of several other proteins in the coming year.
16. REFERENCE
• Voet, Donald; Voet Judith. Biochemistry, 3rd edition, John
Wiley and sons.
• Champe, Pamela.C, Harvey, RichardA, Ferrier Denise R
(2005). Lippincott’s Illustrated Reviews: Biochemistry, 3rd
edition. Lippincott William and Wilkins.
• McKee Trudy, McKee James R (2003), Biochemistry: The
molecular basis of life, 3rd edition, McGraw Hill.
• http://esciencenews.com/articles/2011/06/01/new.antibiotics.a.
step.closer.with.discovery.bacterial.protein.structure
• http://www.eurekalert.org/pub_releases/2010-04/sri-
srs042610.php
• http://www.physorg.com/news/2011-10-cell-survival-protein-
reveals.html
