Polymerase Chain Reaction
"Investigate what PCR is - how has it revolutionised molecular biology and give several examples of how it is used?"
PCR stands for polymerase chain reaction. This is a technique devised by Cary Mullis for cloning genes in a test tube without involving bacteria - and instead uses DNA polymerases (enzymes) to make multiple copies of a DNA strand. The polymerases must be able to function at high temperatures, so the enzymes are usually obtained from thermophilic bacteria such as Thermus aquaticus.
To obtain the DNA, the sample of cells is placed into a solution, and solution is boiled, so the DNA is released. The DNA to be copied is placed in solution, and the temperature of this solution is then raised to 95?c to separate the two strands of DNA. The solution is then mixed with DNA polymerase, and nucleotides. Some short nucleotide sequences which act as a "start" signal for replication (primers) are also added to the solution. The temperature of the solution is slowly lowered to 53?c, to allow primers to bind to DNA. The temperature is then raised again to 73?c to enable thermostable polymerase to replicate DNA. This cycle of temperature changes is repeated about 20 times.
"Investigate what PCR is - how has it revolutionised molecular biology and give several examples of how it is used?"
PCR stands for polymerase chain reaction. This is a technique devised by Cary Mullis for cloning genes in a test tube without involving bacteria - and instead uses DNA polymerases (enzymes) to make multiple copies of a DNA strand. The polymerases must be able to function at high temperatures, so the enzymes are usually obtained from thermophilic bacteria such as Thermus aquaticus.
To obtain the DNA, the sample of cells is placed into a solution, and solution is boiled, so the DNA is released. The DNA to be copied is placed in solution, and the temperature of this solution is then raised to 95?c to separate the two strands of DNA. The solution is then mixed with DNA polymerase, and nucleotides. Some short nucleotide sequences which act as a "start" signal for replication (primers) are also added to the solution. The temperature of the solution is slowly lowered to 53?c, to allow primers to bind to DNA. The temperature is then raised again to 73?c to enable thermostable polymerase to replicate DNA. This cycle of temperature changes is repeated about 20 times.
