A2 OCR Biology: Sequencing and Copying DNA


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Emily Summers
Artificial DNA replication, carried out on small samples of DNA to create many
copies of the sample, useful in forensics. This is called amplification.
Sequencing reaction relies on:
The DNA is made up of antiparallel backbone strands
Made up of strands with a 5' prime and a 3' prime end
Grows from the 3' end only
Complementary base pairing
Primers Short, single stranded DNA sequences about 1020 bases in length,
needed in beginning the sequencing reactions and polymerase chain reactions to
bind to a section of DNA because the DNA polymerase enzymes cannot directly
bind to single stranded DNA fragments.
DNA polymerase is thermophilic as it is not denatured by the extreme temperatures
used in the process, the enzyme is derived from Thermus aquaticus (Taq) a
thermophilic bacterium that is able to grow in hot springs of 90o

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Emily Summers
Start with a sample of the DNA to be amplified, and add the four nucleotides and
DNA polymerase.
Separate strands by heating to 95°C for two minutes. This breaks the hydrogen
DNA polymerisation always requires primers which are separately synthesised
and added at this stage. This means that a short length of the sequence of the
DNA must already be known, but it does have the advantage that only the part
between the primer sequences is replicated.…read more


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