Protein, definition, discovery, classification, importance, structure of protein

1. PROTEIN

2. CONTENT
 WHAT IS PROTEIN
 DISCOVERY OF PROTEIN
 STRUCTURE OF PROTEIN
 CLASSIFICATION OF PROTEIN
 BIOLOGICAL IMPORTANCE of PROTEIN

3. WHAT IS PROTEIN ??
• Proteins are large biomolecules and macromolecules that comprise one or more
long chains of amino acid residues.
• Amino acids are made up of carbon,oxygen,hydrogen and
nitrogen. Sulphur and Phosphorous are also found in some
amino acids too.For example- Sulphur in methionine and
phosphorus in α-Phosphino α-amino acids
• Amino acids contain an amino group (-NH2), a carboxylic
group (-COOH) , a hydrogen and a variable side chain (R) all
connected to a single carbon atom.Different types of amino
acid contain different kind of side chain.There are mainly 20
types of amino acids
• Amino group of one amino acid combine with carboxyl group
of another amino acid resulting in formation of Peptide bond
and release of H2O. A number of amino acids connected
through peptide bond produces protein

4. PEPTIDE BOND FORMATION
PROTEIN CONSISTING OF AMINO ACIDS

5. DISCOVERY OF PROTEIN.
 Proteins were recognized as a distinct class of biological molecules in the
eighteenth century by Antoine Fourcroy and others, distinguished by the
molecules' ability to coagulate or flocculate under treatments with heat or acid.Ex-
Egg albumin
 But Proteins were first described by the Dutch chemist Gerardus Johannes Mulder.
 In 1838 Jöns Jacob Berzelius proposed the name protein which is derived from Greek
word proteios, meaning "primary”. It is named so because proteins play a vital role
in almost all biochemical reactions in an organism. These are also part of
structural components of cells, tissues. For example proteins constitute 12 % of
cell .
GERARDUS JOHANNES MULDER Jöns Jacob Berzelius

6. PROTEIN STRUCTURE
Proteins exist in different forms or structures . These forms include
simple primary structure to complex quaternary form.

7. PRIMARY STRUCTURE
•The Primary structure of proteins is the exact ordering of amino acids forming their
chains.
•The exact sequence of the proteins is very important as it determines the final fold
and therefore the function of the protein.
•The number of polypeptide chains together form proteins. These chains have amino
acids arranged in a particular sequence which is characteristic of the specific protein.
Any change in the sequence changes the entire protein
•Protein can consist of different types of amino acids of varying quantity
•But proteins are not functional in primary form,they are usually active in tertiary or
quaternary form.
•Some proteins like ribonuclease enzyme and hormone insulin only exist in primary
structure.
INSULIN IN PRIMARY FORM

8. SECONDARY STRUCTURE
• Primary structure of protein undergoes folding and coiling to form secondary
structure
• These polypeptide chains usually fold due to the interaction between the amine and
carboxyl group of the peptide link.
•They are found to exist in two different types of structures α – helix and β – pleated
sheet structures.
• In case of α – helix amino acids are so placed that three side chains extend
outwards from the spiral.It is stabilised by hydrogen bonding in between O atom
of –COOH group of one amino acid and –NH group of next 4th amino acid
• In this arrangement, the polypeptide chains are stretched out beside one another and then bonded
by intermolecular H-bonds. In this structure, all peptide chains are stretched out to nearly maximum
extension and then laid side by side which is held together by intermolecular hydrogen bonds. The
structure resembles the pleated folds of drapery and therefore is known as β – pleated sheet
• It can be parallel or anti-parallel type.N atom point of Two chains are arranged
in same order or pointing in same direction.In anti-parallel type chains are
arranged in opposite manner.
• Ex- α – helix type – Keratin in Hair
• Ex- β – pleated sheet- Silk Fibronin

10. TERTIARY STRUCTURE
•This structure arises from further folding of the secondary structure of the protein.
•H-bonds, electrostatic forces, disulphide linkages, and Vander Waals forces(Hydrogen bonding)
stabilize this structure.
•It represents 3-D structure of protein .
•Protein is functional in tertiary structure.
IONIC BOND - ionic bond, also called electrovalent bond, type of linkage
formed from the electrostatic attraction between oppositely charged ions in
a chemical compound.
HYDROGEN BOND - hydrogen bonding, interaction involving
a hydrogen atom located between a pair of other atoms having a
high affinity for electrons(Oxygen,Nitrogen,Flourine). In case of proteins
usually Nitrogen and Oxygen atom are involved in Hydrogen Bonding
DISULPHIDE BOND – A disulfide bond is a covalent bond between two
sulfur atoms (–S–S–) formed by the coupling of two thiol (–SH)
groups

11. IONIC BOND HYDROGEN BONDING
DISULPHIDE BOND

13. QUATERNARY STRUCTURE
• The spatial arrangement of various tertiary structures gives rise to the quaternary structure. Some of
the proteins are composed of two or more polypeptide chains referred to as sub-units. The spatial
arrangement of these subunits with respect to each other is known as quaternary structure.
• H-bonding.ionic bond,hydrophobic bonds maintain structure of quaternary structure
• Ex- Haemoglobin.
• It consists of 2 alpha chains of 141 amino acid and 156 amino acids in two beta chains.A Fe2+ is also
involved with it.
• In tertiary structure and quaternary structure activity of protein is highly regulated by pH, substrate,
ion concentration, temperature etc.
HAEMOGLOBIN

14. CLASSIFICATION OF PROTEIN
• Proteins can be classified into different categories on the basis of different criteria.
Those are on the basis of
1. COMPOSITION
2. FUNCTION
3. SHAPE
4. NATURE

15. SIMPLE
CONJUGATED
COMPOSITION
On hydrolysis it yields only alpha
amino acids. Example-
• Albumin- Found in egg
• Globulins- In Haemoglobins
• Glutenin - Found in Wheat
On hydrolysis it yields non proteinaceous group
called prosthetic group along with amino
acids.It can be further classified into
1. Glycoprotein= Glucose+Protein Mucin, found
in saliva
2. Phosphoprotein= Phosphorous + Protein
Casein, found in milk
3. Chromoprotein= Colouring agent + Protein
Haemoglobin
4. Nucleoproteins= Nucleic acids + Protein-
Nucleohistones
5. Lipoproteins=Lipid+Protein Found in
plasmalemma
MUCIN

16. FUNCTIONS
STRUCTURAL PROTEIN
CONTRACTILE PROTEIN
HORMONE
ENZYME
ANTIBODY
BLOOD PROTEIN
Part of different body structures. Ex-
Collagen,Proteins in skin
Found in muscles. Ex- Actin,Myosin
Chemical Messengers of body.Ex- Insulin
Take part in different biochemical reactions. Serve
as Bio-Catalysts. Ex- Pepsin, Lipase
Globulin Proteins involved in Immuno-response.Ex-
Gamma globulin
Found in blood- Albumin,Fibrinogen,Haemoglobin

17. ACTIN AND MYOSIN IN MUSCLE ANTIBODY

18. SHAPE
 FIBROUS  GLOBULAR
Fibrous proteins contain polypeptide
chains organized approximately in
parallel along a single axis,
producing long fibres or large
sheets. Such proteins tend to be
mechanically strong and resistant
to solubilization in water.
Ex- Keratin in hair, Actin and myosin
of muscle
Globular proteins are named for their
approximately spherical shapes and
are the most abundant proteins in
nature. The globular proteins exist in
an enormous variety of three-
dimensional structures.
Ex- Immunoglobulins

19. FIBROUS GLOBULAR

20. ACIDIC • Proteins rich
in acidic
amino acids
like aspartic
acid,glutamic
acid
BASIC
• Rich in basic
proteins like
Lysine and
Arginine
NATURE OF PROTEIN

21. SOME COMMON PROTEINS AND THEIR FUNCTIONS

22. i. Proteins are the essence of life processes.
ii. They are the fundamental constituents of all
protoplasm and are involved in the structure of
the living cell and in its function.
iii. Enzymes are made up of proteins.
iv. Many of the hormones are proteins.
v. The cement substances and the reticulum
which bind or hold the cells as tissues or organs
are made up partly of proteins.
vi. They execute their activities in the transport
of oxygen and carbon dioxide by haemoglobin
and special enzymes in the red cells.
BIOLOGICAL IMPORTANCE OF PROTEIN

23. vii. They function in the homeostatic control
of the volume of the circulating blood and
that of the interstitial fluids through the
plasma proteins.
viii. They are involved in blood clotting
through thrombin, fibrinogen and other
protein factors.
ix. They act as the defence against infections
by means of protein antibodies.
x. They perform hereditary transmission by
nucleoproteins of the cell nucleus.
BIOLOGICAL IMPORTANCE OF PROTEIN

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