Read the following paragraph carefully and answer the given questions.
In the year 1963 the two enzymes responsible for restricting the growth of bacteriophage in E. coli were isolated. The first restriction endonuclease - Hind II, whose functioning depended on a specific DNA nucleotide sequence was characterized five years later. It was found that Hind II always cut DNA molecules at a particular point by recognizing 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 recognize different recognition sequences.
Hind II is a restriction endonuclease because -
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → It makes cut at specific positions within the DNA.
Option (1) It removes nucleotides from the ends of DNA. — Incorrect. An enzyme that works from the ends of DNA is an exonuclease. Hind II does not nibble at the ends; it cuts inside the DNA molecule.
Option (2) It makes cut at specific positions within the DNA. — Correct. “Endo” means inside. Hind II cuts inside the DNA molecule, and only at the point where it finds its recognition sequence of six base pairs. That is why it is an endonuclease.
Option (3) It recognizes palindromic RNA sequences. — Incorrect. A restriction endonuclease recognises a palindromic sequence in DNA, not in RNA. A DNA palindrome is a sequence of base pairs that reads the same on the two strands when both are read in the same direction, such as GAATTC.
Option (4) It can join any two DNA sequences at specific points. — Incorrect. Joining pieces of DNA is the work of DNA ligase. A restriction enzyme does the opposite job: it cuts DNA.
Note: This passage is taken from NCERT as it is. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
Restriction Enzymes – …
