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.
The primers used in PCR are made up of:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Oligonucleotides
A primer is a short, single-stranded piece of nucleic acid that is made in the laboratory. It is complementary to one end of the region of DNA to be copied. The DNA polymerase needs it as a starting point. Two sets of primers are used in PCR. Since a primer is a short chain of nucleotides, it is an oligonucleotide.
(1) Amino acids — Incorrect. Amino acids are the units of proteins, not of nucleic acids.
(2) Oligosaccharides — Incorrect. These are short chains of sugars. They cannot pair with DNA.
(3) Oligonucleotides — Correct. Short chains of nucleotides can pair with the matching DNA region.
(4) Oligopeptides — Incorrect. These are short chains of amino acids, which are protein pieces.
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:
Amplification of Gene of Interest Using PCR – “PCR stands for Polymerase Chain Reaction. In this reaction, multiple copies of the gene (or DNA) of interest is synthesised in vitro using two sets of primers (small chemically synthesised oligonucleotides that are complementary to the regions of DNA) and the enzyme DNA polymerase. The enzyme extends the primers using the nucleotides provided in the reaction and the genomic DNA as template.”