Denaturation of Proteins Video Lecture | Chemistry Class 12 - NEET

this familiar gelatin dessert actually
is a good example of the process of
coagulation of proteins into a
three-dimensional lattice work that
entraps water molecules to produce a
semi solid gel this animation explains
the physical chemistry behind the
process proteins are synthesized by
polymerizing amino acids the
polymerization occurs by repeatedly
forming peptide bonds that link
individual amino acids together into a
chain there are three structural
features that influence the
three-dimensional shape of a water
soluble protein primary structure is the
peptide bond between individual amino
acids that creates a long chain of
connected amino acids these long chains
of polymerized amino acids have
hydrophobic water repelling and
hydrophilic water attracting projections
that are oriented perpendicular to the
chain as shown in this illustration of a
growing protein chain
secondary structure is the helix that
the protein chain curls into as a result
of hydrogen bonds and other weak forces
tertiary structure is created when the
protein molecules fold back on
themselves outside of the helical
segments to put the hydrophobic portions
to the interior and the hydrophilic
portions to the exterior several helical
regions can exist in different portions
of the molecule when the protein has
folded and refolded to reach its most
stable configuration it will have mostly
hydrophilic amino acid residues on the
exterior and mostly hydrophobic residues
directed into the interior
when natural proteins are subjected to
physical or chemical treatment their
structure changes and they become
unnatural we call that process
denaturation in this example heating the
proteins in solution imparts energy to
the protein molecules this added energy
is enough to break the relatively weak
forces that hold the protein in its
refolded and helical tertiary and
secondary configurations as the process
of denaturation proceeds the protein
molecule unfolds more and more and the
internally directed hydrophobic regions
now become exposed on the outside of the
molecule the peptide bonds are largely
hydrophilic once these segments are set
free from each other they attract water
molecules the recruitment of water
molecules entraps the water molecules in
close proximity to the protein strands
the hydrophobic portions of the
molecules are also exposed this
situation is unfavored because the
hydrophobic portions of molecules are
not stable in an aqueous environment
hence upon unfolding the hydrophobic
regions on individual protein molecules
will associate with hydrophobic regions
on other protein molecules this
situation encourages the association of
these protein molecules into larger and
larger random three-dimensional
structures the molecules aggregate into
very large water insoluble collections
that are quite randomly assembled as the
proteins denature latticework structures
grow amorphous Lea and attract the
solvent water molecules into cell-like
structures the self associated water
molecules in groups adhere to the
surface of hydrophilic regions of the
protein while hydrophobic regions of the
protein dissolve into each other and
provide the energy to retain the
structure as this process continues
irreversibly all of the protein
molecules are recruited to this large
and soluble mass in a randomly organized
structural framework that contains
entrapped water molecules one example of
the consequences
of unfolding and reassociation molecules
is coagulation of egg white frying an
egg is no more complicated than
denaturing the egg white protein the
Assembly of irreversibly denatured
protein molecules results in formation
of a solid gel the gel and traps water
molecules inside the white into a semi
solid structure which holds its shape
under normal conditions other examples
of denatured protein assembling into
three-dimensional structures include the
baking of yeast risen bread coagulation
of meat proteins by cooking in such
products as hot dogs
add in the solidification of gelatin
upon cooling of a solution denaturation
and coagulation of proteins is a complex
irreversible process but the study of
denaturation has allowed us to better
understand the three-dimensional
structure of native proteins