DNA amplification

The information obtained from DNA is extensive whether it be used in forensic investigations or for screening of diseases, prenatal testing or parental testing. Traces of DNA used for such purposes are useful when enough copies of DNA can be obtained so it can be subjected to such testing. The amplification of the DNA is achieved using the Polymerase Chain Reaction (PCR).

 PCR relies on a DNA polymerase to amplify the DNA, the DNA polymerase used is known as Taq polymerase coming from the bacterial species Thermus aquaticus that lives in hot springs so it is able to withstand the high temperatures used in the process of PCR. Taq polymerase operates optimally at higher temperatures unlike other DNA polymerases.

Steps in PCR

Dissociation

The DNA sample is denatured by heating it to 90oC for 2 minutes allowing the strands to dissociate into single strands.

Annealing of the primers

Primers are added that anneal with regions on either end of the DNA sample of interest. This occurs at 55oC for two minutes.

Extension of primers

Taq polymerase uses the primers as a point of initiation and extends them so that two complete double stranded are formed, provided that there is adequate amount of nucleotides available. This occurs at 72oC for one minute.

This process is repeated again to obtained more copies of the DNA.

pcr

Click to enlarge1

Please note temperatures that are described for each process vary depending on what textbook you read. Temperatures given are approximate temperatures and the ones described above are the temperatures that were suggested in the 2012 VCAA Examiner’s Report for VCE Biology Exam 2.

See also


  1. http://en.wikipedia.org/wiki/Polymerase_chain_reaction#/media/File:Polymerase_chain_reaction.svg