[CENTER]التفاعل المتسلسل للبوليميرات
( 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 .[COLOR=red][FONT=Simplified Arabic]
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 .
[B]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 .[COLOR=black][FONT=Simplified Arabic]
Taq Polymerase then synthesizes the complementary strand of DNA , using yhe primer as the starting point .[/font][/color][/b]
[B]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 . [COLOR=black][FONT=Simplified Arabic]
[I][B]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 .[COLOR=black][FONT=Simplified Arabic]
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 .