Polymerase chain reaction

What is the polymerase chain reactionpolymerase chain reaction
PCR is a series of temperature-controlled reactions which enable us to amplify a very tiny sample of DNA, producing enough material for it to be analysed or used in DNA profiling. ?

DNA is the molecule which carries all our inherited information. It has a double helix structure, and is made up of four nucleotidenucleotide
Monomer unit of the nucleic acids DNA and RNA. Each nucleotide is made up of three parts: a pentose sugar, a phosphate group and a nitrogenous base.  bases – adenine, thymine, cytosine and guanine - joined together in pairs. Since the structure and importance of DNA was first recognised over sixty years ago the molecule has been studied by thousands of scientists. One development which has made it much easier for everyone working in the field is the polymerase chain reaction (PCR).

PCR has revolutionised molecular biology and DNA technology. Invented by Kary B Mullis, it enables the production of large quantities of DNA from very small samples in a remarkably short time. This in turn makes it possible for us to analyse tiny samples of DNA and unravel the mysteries of individual genes.

Every time a cell in the body reproduces itself, the DNA in the nucleus is copied. The double helix of the DNA ‘unzips’, and the enzyme DNA polymeraseDNA polymerase
An enzyme involved in the production of a new nucleotide strand to form a new DNA double helix.  makes a copy using the separated strands as templates. For the process to work there must be plenty of nucleotide bases, the small primer sequences which are needed to get the copying process started and the enzyme DNA polymerase.

In 1983 Kary Mullis came up with the idea of using enzymes from a bacterium which lives in the hot springs in Yellowstone National Park to develop a technique for replicating DNA artificially in the lab. His idea worked, and he won a Nobel prize in 1993.

Stage 1:The reactants are mixed together in a PCR vial. The mixture contains the DNA which is to be amplified, the enzyme DNA polymeraseDNA polymerase
An enzyme involved in the production of a new nucleotide strand to form a new DNA double helix. , small primer sequences of DNA and a good supply of the four nucleotidenucleotide
Monomer unit of the nucleic acids DNA and RNA. Each nucleotide is made up of three parts: a pentose sugar, a phosphate group and a nitrogenous base. bases A,T,C and G. The vial is placed in a PCR machine.

Stage 2: The reaction mixture is heated to 90-95^oC for about thirty seconds. At this temperature the DNA strands separate as the hydrogen bondhydrogen bond
An intermolecular attractive force between hydrogen, when it is covalently bonded to a highly electronegative atom (fluorine, oxygen or nitrogen), and an oxygen, nitrogen or fluorine atom on another molecule. s holding them together break down.

Stage 3: The mixture is cooled down to 50-60^oC. At this temperature the primers bind (or anneal) to the single DNA strands. The primers are short sequences of nucleotidenucleotide
Monomer unit of the nucleic acids DNA and RNA. Each nucleotide is made up of three parts: a pentose sugar, a phosphate group and a nitrogenous base. bases which must join to the beginning of the separated DNA strands for the full copying process to start.

Stage 4: In the final step the mixture is heated up again to 75^oC for at least a minute. This is the optimum temperature for the DNA polymeraseDNA polymerase
An enzyme involved in the production of a new nucleotide strand to form a new DNA double helix. enzyme. The enzyme adds bases to the primer segments to build up complementary strands of DNA identical to the original molecule.