Package 2- Polymerase Chain Reaction (PCR)

Polymerase Chain Reaction (PCR) is the quick and easy method for generating unlimited copies of any fragment of DNA. This technique is used mainly in two areas: detection of infectious disease organisms & detection of variations and mutations in genes.

Why is PCR so useful?
The genetic material of each living organism (plant, animal, bacterium or virus) possesses sequences of its nucleotide building blocks (usually DNA, sometimes RNA) are uniquely and specifically present only in its own species. Complex organisms such as human beings possess DNA sequences that are uniquely and specifically present only in particular individuals. These unique variations make it possible to trace genetic material back to its origin, identifying with precision at least what species of organism it came from, and often which particular member of that species.

What PCR requires?
This technique requires a template molecule (the DNA or RNA you want to copy) and two primer molecules to get the copying process started. The primers are short chains of the four different chemical components that make up any strand of genetic material. These four components are like bricks or building blocks that are used to construct genetic molecules; also known as nucleotides or bases in laboratory. For PCR, primers must be duplicates of nucleotide sequences on either side of the piece of DNA of interest, which means that the exact same order of the primers’ nucleotides must be known already.

Procedures of PCR:
There are 3 basic steps in PCR.

1st step --> The target genetic material must be denatured, where the strands of its helix must be wound and separated by heating to 90-96°C.

2nd step --> Hybridization/annealing, where the primers bind to their complementary bases on the now single-stranded DNA.

3rd step --> DNA synthesis by a polymerase. Starting from the primer; the polymerase can read a template strand and match it with a complementary nucleotides very quickly.

The result is two new helixes in place of the first, each composed of one of the original strands plus its newly assembled complementary strand.



Quoted from: http://www.faseb.org/opa/bloodsupply/pcr.html