Different structure of proteins and the classifications according to it .Explanation with structure and arranges in sequence

2. INTRODUCTION
 Proteins are important class of biological
macromolecules which are the polymer of amino acid
 There are several levels of structural organisation of
proteins . They are :-
i. Primary structure
ii. Secondary structure
iii. Tertiary structure
iv. Quarternery structure

5. Essential Conditionally essential Non-essential
Histidine (H) Arginine (R) Alanine (A)
Isoleucine (I) Cysteine (C) Aspartic acid (D)
Leucine (L) Glutamine (Q) Asparagine (N)
Lysine (K) Glycine (G) Glutamic acid (E)
Methionine (M) Proline (P) Serine (S)
Phenylalanine (F) Tyrosine (Y) Selenocysteine (U)
Threonine (T) Pyrrolysine* (O)
Tryptophan (W)
Valine (V)

6. PRIMARY STRUCTURE
 The primary structure
of protein refers to the
sequence of amino acid
present in a
polypeptide chain
 Amino acid are
covalently linked by
peptide bond
 Peptide bond is
formed by the removal
of one water molecule .
 The 10 structure of
protein start from the
amino terminal (N) end

7.  To predict the 2o and 30
structure from sequence
homologies with related
protein .
 Many genetic disease arise
from abnormal amino
acid sequence
 To understand the
molecular mechanism of
action of protein
 To find the evolutionary
path
 Gene sequencing method .
 Edman degradation - the
amino terminal residue is
labeled and cleaved from
the peptide without
disrupting the peptide
bonds between other
amino acid residues.
IMPORTANCE OF PRIMARY
STRUCTURE
METHOD OF AA
SEQUENCE
DETERMINATION

8. SECONDARY STRUCTURE
 Localized arragement of adjacent AA formed as the polypeptide
chain folds
 Alpha helices are the most common form of secondary structure
formed by the right hand coiling of the primary structure of the
protein
 Coiling is caused by the H bond interaction between the AA of
the protein
 Secondary structure consist of :-
 a Helix
 b pleated sheet
 b bends
 Super secondary structure

13. BETA BENDS
 Permits the change of the
direction of the peptide
chain to get a folded
structure
 It gives protein globularity
rather than linearity
 H bond stablizes the beta
turn structure
 Proline and glycine are
frequently found in beta
turns
 Beta turns often promote
the formation of
antiparallel beta sheets

14. SUPER SECONDARY STRUCTURE
 Present in Globular
protein
 This structure form
when two b pleated
sheath are connected
to each other by an
alpha helix
 Example :- b-a-b
supersecondary motif

15. 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 upon on its
tertiary structure if this is
disrupted, it loses its
activity .

16. INTERACTIONS STABILIZING 30
STRUCTURE
 The final shape is
determined by variety
of bonding interaction
between the side chain
of the amino acid
• Hydrogen bond
• Ionic bond
• Disulphide bridges
• Hydrophobic
Interactions

17. DETERMINATION OF THE TERTIARY
STRUCTURE
 The protein structure can be studied through :-
• X- ray crystallographic studies
• Nuclear magnetic resonance
 Most of the structure is deposited in a database
known as protein database bank (PDB) ,it allows the
tertiary structure of variety of proteins to be
analyzed and compared

18. QUATERNARY STRUCTURE
 Biological function of
some molecules is
determined by multiple
polypeptide chains –
multimeric proteins
 Arrangment of
polypeptide sub unit is
called as quaternary
structure
 Sub unit are held together
by non covalent
interactions
 Eg - Heamoglobin (a2b2)

19. CLASSIFICATION BASED ON SHAPE
 Depending upon the axial ratio protein has been
classified into two types :-
I. Fibrous protein
II. Globular protein

20. FIBROUS PROTEIN
 Axial ratio more than 10
 Long thread like molecule
 Their helical strand mainly forms fibres
 These protein are insoluble in water
 Form structure of the tissue
 Present where support is required
 Example :- collagen , elastin , keratin

21. GLOBULAR PROTEIN
 Axial ratio less than 10
 Spheroid or ovoid in shape
 Enzymes are mostly globular in shape
 Subdivide into two types of protein :-
I. Albumin : soluble in water
II. Globulin : soluble in dilute salt solution

22. CLASSIFICATION BASED ON FUNCTION
 Catalytic protein :- These are the enzyme which may be simple
or conjugated
I. Alkaline phosphotase
II. Alanine Transaminase
 Regulatory or Hormonal protein :- Many protein acts as
hormone
I. Insulin
II. Growth Hormone
 Structural protein :- Contribute to the structure of tissue
I. Collagen
II. Elastin

23.  Transport protein :- Serve to carry substances
I. Transferrin carry iron
II. Heamoglobin carry oxygen
 Immune protein :- Serve in the defence mechanism
I. Immunoglobulin - IgA , IgG , IgM , IgE , IgD
 Contractile protein :- Takes part in muscle
contraction
I. Actin
II. Myosin

24.  Genetic protein :- Protein present in combination
with nucleic acid
I. Histone protein
 Storage protein :- To store protein for nutritional
purpose
I. Casein in milk
II. Glaidin in wheat