Presentation on theme: "Polymerase Chain Reaction Mrs. Stewart Medical Interventions."— Presentation transcript:
Polymerase Chain Reaction Mrs. Stewart Medical Interventions
Polymerase Chain Reaction a lab technique that produces numerous copies of a specific segment of our DNA in a relatively short period of time. three-step process repeated over and over produces identical copies of the target sequence.
Extension The temperature of the sample is heated to between 72-75 o C, which is the optimal temperature for the Taq polymerase enzyme to function. Taq polymerase binds and extends a complementary DNA strand from each primer (adding approximately 60 bases per second, using the free-floating nucleotides)
As amplification proceeds, the DNA sequence between primers doubles after each cycles (The amplification of the target sequence proceeding in an exponential fashion ( 1 2 4 8 16................) up to million of times the starting amount until enough is present to be seen by gel electrophoresis.
How many cycles? Most PCRs should include only 25 – 35 cycles. Depends on the amount of starting material
Advantages of PCR Useful, non-invasive procedure Simplicity of the procedure Sensitivity of the PCR Disadvantages of PCR False positive results (cross contamination). False negative results (e.g. rare of circulating fetal cells).