Question

The given figure shows three steps (A, B, C) of Polymerase Chain Reaction (PCR). Select the option giving correct identification together with what it represents?

• A. A- Denaturation at a temperature of about ${50}^o$C
• B. C- Extension in the presence of heat stable DNA polymerase
• C. A- Annealing with two sets of primers
• D. B- Denaturation at a temperature of about ${98}^o$C separating the two DNA strands

Answer 1

Answer: (B)

C- Extension in the presence of heat stable DNA polymerase

Polymerase chain reaction (PCR) is the process in which the amplification of the gene of interest is carried out with two sets of primers and a thermostable DNA polymerase enzyme Taq polymerase. The process involves the following steps:

• Denaturation: The double-stranded DNA is heated up to 98${}^o$ C which causes the hydrogen bonds to break and the two strands get separated.
  
• Annealing: The two sets of primers are added which bind to the appropriate complementary segment of DNA strand at temperature of about 50${}^o$ C.
  
• Extension: The Taq polymerase enzyme polymerizes the nucleotide chain using the nucleotides provided in the medium and by using the template strand. This reaction is carried out at the temperature of about 72${}^o$ C.
• Thus, the correct answer is option B.