Question

44) Often before performing tests to identify unknown bacteria, this has to be performed to make copies of the DNA of interest A) genetic fingerprinting B) slide agglutination C) western blot D) polymerase chain reaction (PCR) E) DNA CHIP

Answer 1

Before performing any test to identify the unknown bacteria, first, the number of copies should be increased. The best method to increase the number of copies is PCR and specifically for bacteria, we can use colony PCR.

PCR is a technique in which a large number of copies are generated with the help of very less amount of DNA. That's why this technique is also used in forensic to amplify the small DNA found at crime scene.

• Denaturation(94°C): This technique is very much temperature-dependent. The instrument thermocycler is used to carry out the reaction. In this reaction first, the DNA is denatured it means the double-stranded DNA is converted to the single-stranded DNA.
• Annealing (65°C): After the denaturation, the next step is Annealing, in this step the primers and nucleotides are added to the template so the primers hybridize with the template.
• Elongation (74°C): The last step is elongation step, in this step, the Taq polymerase is used for the polymerization, Taq polymerase is a Thermo resistant polymerase which polymerizes the nucleotide even at a very high temperature without degradation. The Taq polymerase bind to the 3'-OH of the primer and starts for the further addition of a nucleotide. These steps are carried out continuously for 35 cycles in which the final product is highly amplified.

In the case of bacteria, the colony is taken directly from the plate and the specific DNA is amplified which is only present in the specific bacteria. Then the above steps are used to amplify the DNA and this process is known as colony PCR.