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3. DNA polymerase proceeds along a
single‑stranded molecule of
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DNA, recruiting
free dNTP's
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(deoxy‑nucleotide‑triphosphates)
to hydrogen bond with their
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appropriate
complementary dNTP on the single strand (A with T and
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G
with C), and to form a covalent phosphodiester bond with the
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previous
nucleotide of the same strand. The energy stored in the
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triphosphate
is used to covalently bind each new nucleotide to the
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growing
second strand. There are different forms of DNA polymerase ,
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but
it is DNA polymerase III that is responsible for the processive
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synthesis
of new DNA strands. DNA polymerase cannot start
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synthesizing
de novo on a bare single strand. It needs a primer with a
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3'OH
group onto which it can attach a dNTP. DNA polymerase is
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actually
an aggregate of several different protein subunits, so it is often
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called
a holoenzyme. The holoenzyme also has proofreading
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activities,
so that it can make sure that it inserted the right base,
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and
nuclease (excision of nucleotides) activities so that it can cut
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away
any mistakes it might have made.
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