Bsc biotechnology topic polymerase chain reaction ( PCR)
The polymerase chain reaction (PCR) is a widely used technique in molecular biology that allows for the amplification of specific DNA sequences. Here's a brief overview of the PCR process:
Denaturation: The DNA sample containing the target sequence is heated to a high temperature (typically around 94-98°C), causing the double-stranded DNA to separate (denature) into single strands.
Annealing: The reaction mixture is cooled to a lower temperature (around 50-65°C), allowing short DNA primers to bind (anneal) to the complementary regions on each of the single DNA strands. These primers are designed to flank the target sequence and serve as starting points for DNA synthesis.
Extension: A heat-stable DNA polymerase enzyme, such as Taq polymerase, synthesizes new DNA strands by extending from the primers. The reaction mixture is heated to a temperature optimal for the DNA polymerase (around 72°C), and it adds complementary nucleotides to the primers, synthesizing new DNA strands that are complementary to the template strands.
Cycling: Steps 1 to 3 are repeated for multiple cycles, typically 25 to 35 times, in a specialized thermal cycler machine. Each cycle doubles the amount of DNA, resulting in an exponential amplification of the target sequence. The DNA strands produced in the previous cycle become templates for the subsequent cycles.
By the end of the PCR process, the target DNA sequence has been amplified to a detectable level, even if it was present in very small quantities in the original sample. The amplified DNA can then be used for various applications, such as DNA sequencing, genetic testing, cloning, or analysis of gene expression.
Applications of pcr-
1 diagnosis of pathogens- there are many pathogens that grow slowly. Therefore their cellsare found in less number in the infected cells. Hence for their diagnosis pcr is used.
2 diagnosis of specific mutation- In humans there are thousands of genetic diseases. By using pcr sickle cell anaemia, phenylketonuria can also be detected.
3 dna fingerprinting- dna fingerprinting is more succesfully used in forensic science to serach out criminals, rapists, disputed parentage. This is done through making link between the dna recovered from the sample blood, semen,hairs etc. at the spot of the crime and the dna of suspected indiiduals or between child and his/her parents relatives.