While replicating, the entire DNA molecule
to keep the whole molecule stabilized does not open in one go because it would
be highly expens energetically. Actually unwiding creates tension in the
molecule as uncoiled parts.
Actually, unwinding creates tension in
the molecule as uncoiled parts start forming super coils due to the interaction
of exposed nucleotides.
Instead, helicase enzyme acts on
the double strand at on site (origin of replication) and a small stretch is
unzipped. Immediately, it is held and stabilized by single strand binding
Slowly with the help of enzymes,
exposed strands are copied as a point of unwinding move sand ahead in both
It gives an appearance of
Y-shaped structure which is called replication fork.
The two functions that the
monomer units of NTPs play are
(i) They pair up with exposed
nucleotides of the template strand and make phosphodiester linkages and release
(ii) Hydrolysis of this
pyrophosphate by enzyme pyrophosphatase releases energy that will facilitate
making hydrogen bonds between free nucleotides and bases of the template strand.
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