Molecular scissors
Read the following passage carefully and answer the given questions.
Hind II always cut DNA molecules at a particular point by recognising a specific sequence of six base pairs. This specific base sequence is known as the recognition sequence for Hind II. Besides Hind II, today we know more than 900 restriction enzymes that have been isolated from over 230 strains of bacteria each of which recognises different recognition sequences. The convention for naming these enzymes is the first letter of the name comes from the genus and the second two letters come from the species of the prokaryotic cell from which they were isolated, e.g., EcoRI comes from Escherichia coli RY 13. Restriction enzymes belong to a larger class of enzymes called nucleases. These are of two kinds: exonucleases and endonucleases. Each restriction endonuclease functions by inspecting the length of a DNA sequence. Once it finds its specific recognition sequence, it will bind to the DNA and cut each of the two strands of the double helix at specific points in their sugar-phosphate backbones.
Which one of the following is not a tool of recombinant DNA technology?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Permease
Recombinant DNA technology joins a gene of interest to a vector and puts it into a host. Its key tools are restriction enzymes, polymerase enzymes, ligases, vectors and the host organism.
(1) Vector and host organism — A tool of recombinant DNA technology. The vector carries the gene of interest, and the host cell takes up the recombinant DNA and multiplies it.
(2) Restriction enzyme — A tool of recombinant DNA technology. It cuts DNA at specific sites, like a pair of molecular scissors.
(3) Permease — Not a tool of recombinant DNA technology. Permease is a protein coded by the y gene of the lac operon. It lets lactose enter the bacterial cell. It is not used to cut or join DNA.
(4) Ligase — A tool of recombinant DNA technology. DNA ligase joins the gene of interest to the cut vector.
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:
Tools of Recombinant DNA Technology – “Now we know from the foregoing discussion that genetic engineering or recombinant DNA technology can be accomplished only if we have the key tools, i.e., restriction enzymes, polymerase enzymes, ligases, vectors and the host organism.”
The Lac Operon – “… The y gene codes for permease, which increases permeability of the cell to β-galactosides.”