PCR
Read the following passage carefully and answer the given questions.
In PCR multiple copies of the gene of interest is synthesised in vitro using two sets of primers and the enzyme DNA polymerase. The enzyme extends the primers using the nucleotides provided in the reaction and the genomic DNA as template. If the process of replication of DNA is repeated many times, the segment of DNA can be amplified to approximately billion times, i.e., 1 billion copies are made. Such repeated amplification is achieved by the use of a thermostable DNA polymerase, which remain active during the high temperature induced denaturation of double stranded DNA. The amplified fragment if desired can now be used to ligate with a vector for further cloning.
Taq polymerase used in PCR is a type of -
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → DNA dependent DNA polymerase
Taq polymerase is the thermostable DNA polymerase used in PCR. It comes from the bacterium Thermus aquaticus. A DNA polymerase uses a DNA template to join nucleotides into a new DNA strand, so it is a DNA-dependent DNA polymerase. It stays active at the high temperature that separates the DNA strands.
(1) RNA dependent DNA polymerase — Incorrect. This enzyme makes DNA from an RNA template. PCR copies DNA, not RNA.
(2) DNA dependent RNA polymerase — Incorrect. This enzyme makes RNA from a DNA template. It works in transcription.
(3) DNA dependent DNA polymerase — Correct. It makes DNA on a DNA template.
(4) DNA independent DNA polymerase — Incorrect. No such enzyme is known. A DNA polymerase always needs a template.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
The Machinery and the Enzymes – …
