BIOLOGICAL MOLECULES (Protein)
Protein (Classes, Physical and Chemical Properties, grouping)
Fact!
(i) Primary structure
(refers to
the sequence of
amino acids joined
by peptide bonds in a polypeptide chain. )
(ii) Secondary structure
§ Regular pattern of coiled or folded
poplypeptide chain
§Maintained by hydrogen
bonds between CO
-group of one
amino acid and NH
-group of another.
§Alpha - helix formed from coiling of
a polypeptide chain.
§ Beta - pleated sheet formed from
folding of a polypeptide chain.
§Fibrous proteins - which are
insoluble in water consist of proteins of secondary structures.
§Fibrous proteins
perform structural function
for examples, keratin in hair
and nails, collagen in tendon.
·Tertiary Structure
§Refer to
specific and precise
three dimensional compact
structure formed
from folding and coiling of polypeptide chain.
§With interaction between R groups/ side
chains.
§Maintained byhydrogen bonds, disulphidebonds and hydrophobic interactions.
oDisulfidebond is between cysteine
amino acids.
oHydrogen bond is between polar groups
amino acids
oIonic bond is between ionised amino
group and ionised carboxylgroup
oHydrophobicinteraction is between
non polar side chains
§Is globular with spherical shape
§Soluble in
water with hydrophilic
/ polar groups
facing to
outside
§Tertiary structure
is important for
the functions of
soluble proteins such as enzymes, hormones and antibodies.
·Quaternary Structure
§Formed from
the association of
more than one
polypeptide
chains.
§Haemoglobin is
an example of globular
protein having
quaternary
structure
§Haemoglobin is
made up of
four polypeptide chains
held together by
oDisulfide bond is between cysteine
amino acids
oHydrogen bond is between polar groups
oIonic
bond is between
ionised amino acids
and ionised carboxyl groups
oHydrophobic interaction
is between non-polar
side chains
§Each
polypeptide chain of
haemoglobin has a
haem group or prosthetic group containing
iron atom for binding to
oxygen molecules.
§Collagen is
an example of
fibrous protein having
quaternary structure
§In
collagen, there are
3 polypeptides in
the form of
helix maintained by hydrogen bonds
§Adjacent collagen molecules are linked
by covalent bonds
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