In the context of recombinant DNA technique, what does the term "vector" refer to?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A carrier molecule, often a small DNA molecule, used to transfer a specific piece of DNA (the donor DNA) into the host cell.
In recombinant DNA technology, a gene of interest (the donor or alien DNA) has to be carried into a host cell, such as a bacterium. The carrier used for this is called a vector. Plasmids, the small circular DNA molecules of bacteria, and viruses are used as vectors.
Option (1) Donor DNA, identified and picked up through electrophoresis — Incorrect. The donor DNA is the piece being carried, not the carrier. Electrophoresis is used to separate and pick out DNA fragments, but the fragment picked out is the passenger, not the vector.
Option (2) A carrier molecule, often a small DNA molecule, used to transfer a specific piece of DNA (the donor DNA) into the host cell. — Correct. A vector is a carrier DNA molecule, often a small plasmid, that takes the linked piece of donor DNA into the host cell. There, the vector’s origin of replication lets the linked DNA multiply.
Option (3) Collection of the entire genome in the form of a plasmid — Incorrect. A vector carries one piece of DNA linked to it, not the entire genome. A plasmid is an autonomously replicating, circular, extra-chromosomal DNA; a collection of a whole genome is not what the term vector means.
Option (4) Enzyme that cuts the DNA at specific sites — Incorrect. An enzyme that cuts DNA at specific sites is a restriction endonuclease, the “molecular scissors”. It cuts the vector and the donor DNA, but it is a tool, not the carrier.
NCERT Extract:
Principles of Biotechnology – “… The cutting of DNA at specific locations became possible with the discovery of the so-called ‘molecular scissors’– restriction enzymes. The cut piece of DNA was then linked with the plasmid DNA. These plasmid DNA act as vectors to transfer the piece of DNA attached to it. You probably know that mosquito acts as an insect vector to transfer the malarial parasite into human body. In the same way, a plasmid can be used as vector to deliver an alien piece of DNA into the host organism.”