Biology Polymerase chain reactions.

These cards explain why the PCR is needed, and the process of it. Polymerase chain reactions play a big part on DNA profiling.

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What is it?

To allow forensic scientists to use tiny amounts of DNA they find, such as droplets of hair or skin, the DNA is copied numerous amounts of times using the PCR. the process uses DNA primers which are short DNA sequences complementary to the DNA adjacent to the Short tandem repeat sequence. the primers are marked with fluorescent tags, and the sample is placed in a reaction tube with DNA polymerase, the primers and nucleotides. once in the machine, the tube undergoes a cycle of different temperatures. the first temperature seperates the double stranded DNA, the second optimises prime binding to the target DNA sequence , the polymerase attaches and replication occurs. the third temperature is the optimum temperature for the heat stable DNA polymerase.

as the cycle continues, huge numbers of the DNA fragments are reproduced.

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The temperatures and the occurences.

the first temperature is at 95 degrees. a sample of DNA is treated with detergent to break open the cells and release the DNA, and is mixed with the ingredients mentioned earlier. at this temperature the DNA seperated into two strands.

the second temperature is at 55 degrees. the primers attach at the start of the STR repeated sequence.

and in the third temperature of 70 degrees the DNA polymerase attaches, the nucleotides are added, which extends the DNA from the primer. the STR repeated sequence and the DNA adjacent is replicated.

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The second cycle of PCR.

The temperatures stay the same, in the exact same order.

at 95 degrees, the DNA strands seperate. and at 55 degrees the primers attach at the start of the STR sequence. at 70 degrees the replication occurs from each primer. and in each cycle that follows the process is repeated producing copies that are just the STR sequence fragment. millions of these fragments are created which can then be seperated out by gel electrophoresis.

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Thanks for this! Very useful!

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