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.
Restriction enzymes belong to a larger class of enzymes called as -
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Nucleases
The passage says that restriction enzymes belong to a larger class of enzymes called nucleases. Nucleases break the bonds between the nucleotides of a nucleic acid. They are of two kinds. Exonucleases remove nucleotides from the ends of the DNA. Endonucleases cut at specific positions within the DNA. Restriction enzymes are endonucleases.
(1) Isomerases — Incorrect. Isomerases change a molecule into its isomer. They do not cut DNA.
(2) Nucleases — Correct. Restriction enzymes cut DNA, so they are nucleases.
(3) Transferases — Incorrect. Transferases move a group from one molecule to another. They do not cut DNA.
(4) Ligases — Incorrect. Ligases do the opposite job. DNA ligase joins the cut ends of DNA, for example when a DNA fragment is joined to a 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.