Polymerase  Chain Reaction (PCR)

Polymerase chain reaction enables large amounts of DNA to be produced from very small samples (0.1ml).There is a repeating cycle of separation of double DNA strandsand synthesis of a complementary strand for each.

PCR is a simple process that can be summarized as follows:

The Sample DNA, nucleotides, DNA primers and thermostable DNA polymerase are placed in PCR machine. Then the strands of sample DNA are separated by heating to 95^oC then the mixture is cooled to 37^oC to allow primers to bind. This Mixture is then heated to 72^oC for replication (this is the optimum temp of DNA polymerase). This cycle is repeated many times (~8mins /cycle).

There are certain limitations to the process of PCR for example the separation is achieved by heating to DNA strands to 95^oC while there is no suitable helicase for this purpose. DNA polymerase can’t work on completely single stranded DNA so double stranded regions are needed at the start of sequence to be copied. The primers (short sequences DNA) complementary to bases at start of region to be copied are to be used and to synthesize primers, base sequence at start must be known.

PCR has got a variety of uses some of which are:

·         PCR is used for the detection of infectious agents such as HIV, hepatitis, HPV, EBV, malaria and anthrax
·         PCR is a very value able tool of the diagnosis of certain mutation leading to certain cancers in our body. Is has been used as a prognostic tool for leukemias.
·         PCR is now a day also used to detect genetic abnormalities in post natal or even in in utero periods. Parental testing can also be done using PCR.