Read the following passage carefully.
Restriction enzyme
Restriction enzymes cut the strand of DNA a little away from the center of the palindrome sites, but between the same two bases on the opposite strands. This leaves single stranded portions at the ends. There are overhanging stretches called sticky ends on each strand. These are named so because they form hydrogen bonds with their complementary cut counterparts. This stickiness of the ends facilitates the action of the enzyme DNA ligase. The word palindromes refer to group of letters that forms the same words when read both forward and backward. Restriction endonucleases are used in genetic engineering as molecular scissors.
Palindromes are:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → The same group of letters when read both forward and backward
A palindrome is a group of letters that forms the same word whether read forward or backward, e.g. MALAYALAM. In DNA, a palindrome is a stretch of base pairs that reads the same on the two strands when both are read in the same direction, e.g. 5′-GAATTC-3′ and 3′-CTTAAG-5′. Restriction enzymes recognise such sequences and cut there.
Option (1) The same group of letters when read both forward and backward — Correct. This is the passage’s own definition: the same word in both directions.
Option (2) The different group of letters when read both forward and backward — Incorrect. If the letters change on reading backward, the sequence is not a palindrome.
Option (3) Same group of letters when read only forward — Incorrect. Any word reads the same when read forward again. A palindrome needs both directions to match.
Option (4) Same group of letters when read only backward — Incorrect. Reading in one direction only says nothing about symmetry. The forward and backward readings must agree.
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.