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the polymerase chain reaction (the steps (1 (the DNA sample is mixed with…
the polymerase chain reaction
relies on:
DNA is made up of 2 antiparallel strands
each strand of DNA has 3' and 5' ends
base pairs pair up according to complimentary base pairing theory
DNA only grows from the 3' end
PCR is different from DNA replication in that:
a primer is required to start the process
a cycle of heating and cooling is required
only short DNA sequences can be replicated - not whole chromosomes
the steps
1
the DNA sample is mixed with free nucleotides, primers, magnesium ions and the enzyme Taq DNA polymerase
2
the mixture is heated to around 95 degrees to break the h bonds between bases. this denatures the DNA into two separate strands
3
the mixture is cooled to 68 degrees so primers can anneal to one end of each single strand - preventing h bonds being remade at one end.
4
Taq DNA polymerase enzymes now bind to the double stranded end of the DNA
5
the temperature is raised to 72 - the enzymes optimum - keeping the DNA as single strands
6
polymerase catalyses the addition of new nucleotides to the single stranded DNA (beginning at the end with the primer
7
the process is repeated fro multiple cycles
applications of PCR
tissue typing
detection of oncogenes
detecting mutations
identifying viral infections
monitoring the spread of an infectious disease
forensic science
research