[CENTER][B]التفاعل المتسلسل للبوليميرات[/B]
( Polymerase Chain Reaction )[/CENTER]
The Polymerase chain reaction is a method for making many copies of a specific segment of DNA , starting with a very small amount .
This technique can be used to identify specific microorganisms from a small amount of DNA and to identify persons involved in crimes from DNA on Cigarettes in a single hair follicle .
The DNA to be amplified is mixed with deoxyribonucleotides , a thermal stable DNA polymerase called Taq Polymerase and DNA primers .
The mixture is heated to break the hydrogen bonds in the DNA , forming single- started molecules . The mixture is then cooled sufficiently to allow the DNA primers to anneal to each end of the segment to be copied .
[I]Taq Polymerase then synthesizes the complementary strand of DNA , using yhe primer as the starting point .[/I][/B]
[B][I]The temperature is raised again to separate the DNA stands and then lowered sufficiently to allow the primers to attach . Taq Polymerase now synthesizes another set of new complementary strands . [/I]
[B][I]This process is repeated until enough DNA has been produced to be identified or used for further research . After twenty-one cycles , one molecules of DNA can be amplified to over a million copies .
This amount of amplification can be achieved by running the reaction overnite in a thermal cycle , an instrument that automatically raises and lowers the temperature at appropriate time intervals .
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