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Explain the Polymerase Chain Reaction

1. DNA must be extracted from cells using detergent. The detergent breaks downt the cells releasing the DNA.

2. Add DNA polymerase, DNA primers, and free nucleotides to DNA in a test tube. These components will be used in the PCR process to create new strands of DNA.

3. Put this into a PCR machine where the environment for the reaction can be controlled.

4. Heat to 95 degrees. At this temperature the DNA will denature, splitting the double standed DNA by breaking thy hydrogen bonds holding the bases together. This results in two separate strands with exposed bases.

5. Lower the temperature to 55 degrees. At this temperature teh DNA primers will attach to their complementary sequences of bases. This is called annealing. The primers signal the start of the target sequence you want to replicate. This either is the start of the STR (Short Tandem Repeats) sequence, or a longer sequence that contains the STR sequence.

6. Increase the temperature to 70 degrees. At this point the DNA polymerase will atach to the target sequence and begin forming a new strand of DNA by creating phosphodiester bonds between the free nucleotides that have been paired with the original strand of DNA. This process is called extension.

This process is continued for a long time until there are millions of replications of DNA that can be used for a DNA profile or any other uses.

If STR specific primers are used then the STR sequence would hvae been replicated already. If this isnt the case, then restriction enzymes will be used to "cut out" the STR sequence from the replicated DNA.

Zoe B. GCSE Psychology tutor, A Level Psychology tutor, GCSE Biology ...

4 months ago

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