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A study of pcr or polymerase chain reaction

It was first developed in the 1980s.

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He was awarded the Nobel Prize in Chemistry in 1993 for his pioneering work. PCR is a common tool used in medical and biological research labs. How does PCR work? We will explain exactly what each of these do as we go along.

PCR involves a process of heating and cooling called thermal cycling which is carried out by machine. There are three main stages: Extending — when the temperature is raised and the new strand of DNA is made by the Taq polymerase enzyme.

These three stages are repeated 20-40 times, doubling the number of DNA copies each time. A complete PCR reaction can be performed in a few hours, or even less than an hour with certain high-speed machines.

What is PCR (polymerase chain reaction)?

After PCR has been completed, a method called electrophoresis can be used to check the quantity and size of the DNA fragments produced. Illustration showing the main steps in the polymerase chain reaction PCR. The high temperature causes the hydrogen bonds between the bases in two strands of template DNA to break and the two strands to separate. It is important that the temperature is maintained at this stage for long enough to ensure that the DNA strands have separated completely.

This usually takes between 15-30 seconds. The primers are designed to be complementary in sequence to short sections of DNA on each end of the sequence to be copied.

Polymerase chain reaction

Primers serve as the starting point for DNA synthesis. Only once the primer has bound can the polymerase enzyme attach and start making the new complementary strand of DNA from the loose DNA bases.

This step usually takes about 10-30 seconds. Taq DNA polymerase is an enzyme taken from the heat-loving bacteria Thermus aquaticus. The bacteria's DNA polymerase is very stable at high temperatures, which means it can withstand the temperatures needed to break the strands of DNA apart in the denaturing stage of PCR.

The duration of this step depends on the length of DNA sequence being amplified but usually takes around one minute to copy 1,000 DNA bases 1Kb.

These three processes of thermal cycling are repeated 20-40 times to produce lots of copies of the DNA sequence of interest. The result is a huge number of copies of the specific DNA segment produced in a relatively short period of time.