As easy as PCR - biotech for everyone!

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WHAT IS IT?

A way of increasing the number of copies of a specific region of DNA that you want to study.

Once you know the region of DNA that is of interest, you need to find it to analyse it further. With around 3 billion bases making up human DNA (for example), finding the area you are interested in (made up of say 200 bases) can be a very hard task (like looking for a needle in a haystack!).

In order to make the search easier we can increase the number of copies of the ‘interesting’ area using PCR, (a bit like increasing the number of needles so they are easier to find in the haystack).

How It Works

PCR stands for Polymerase Chain Reaction, and using some specific, and generic chemicals, and heating and cooling we can finish with billions of copies of the area of DNA under study.

Main steps to the PCR process:

1. Denaturation: The 2 DNA strands become un-bound from each other and separate.

2. Annealing (binding primers): Primers – small pieces of DNA specific to the ends of the area of interest - bind to the ends of the target region, identifying the area of interest.

3. Extension (copying and extending the DNA): This means adding free nucleotides* onto the end of the primers to extend the (complementary) strands of DNA (making new, identical DNA).

Steps 1 - 3 are continuously repeated until, after about 30 cycles, there will be approximately 1 billion copies of the DNA region of interest.

*nucleotide: single phosphate-sugar-base unit, a string of nucleotides forms one strand of DNA, (two complementary strings twist together to form the double helix). Free nucleotides are added to the reaction mix as dNTPs.

All of this can be performed in a thermal cycler, such as the Edvotek Edvocycler Junior (BT200806).

Once you have put the ingredients into the microtubes, the thermal cycler will do the rest, leaving you with a sample that you can visualise, by performing electrophoresis (a sort of biotechnology chromatography): loading the samples into a gel through which they travel according to size.

Sample loaded into wells

Our

DNA size reference (each line represents DNA of a known number of base pairs, so you can identify the size of your sample)

Amplified DNA sample

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