Question: 103: Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) :
When a particular restriction enzyme cuts strand of DNA, overhanging stretches or sticky ends are formed.
Reason (R) :
Some restriction enzymes cut the strand of DNA a little away from the centre of palindromic site.
In the light of the above statements, choose the correct answer from the options given below :
(1) Both (A) and (R) are correct and (R) is the correct explanation of (A)
(2) Both (A) and (R) are correct but (R) is not the correct explanation of (A)
(3) (A) is correct but (R) is not correct
(4) (A) is not correct but (R) is correct
Answer: Option (1)
Explanation:
Restriction enzymes are molecular scissors that cut DNA at specific nucleotide sequences known as palindromic sites.
When certain restriction enzymes act on DNA, they do not cut both strands at exactly the same position.
Instead, these enzymes cut the DNA strands a little away from the centre of the palindromic sequence.
This unequal cutting produces short single-stranded extensions at the ends of the DNA fragments.
These single-stranded extensions are called overhanging stretches or sticky ends.
Sticky ends are important because they can easily form hydrogen bonds with complementary sequences during recombinant DNA formation.
Thus, the assertion is correct, and the reason correctly explains why sticky ends are formed.
Therefore, the correct answer is Option (1).