Assertion (A): Restriction enzyme digestions are performed by incubating purified DNA molecules with the restriction enzyme at the optimal conditions for that specific enzyme.
Reason (R): Agarose gel electrophoresis is employed to check the progression of a restriction enzyme digestion.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Both (A) and (R) are correct but (R) is not the correct explanation of (A).
Assertion (A): Restriction enzyme digestions are performed by incubating purified DNA molecules with the restriction enzyme at the optimal conditions for that specific enzyme. — True. A is about how the digestion is carried out. Each enzyme works best under its own conditions, so the purified DNA is kept with the enzyme under those conditions.
Reason (R): Agarose gel electrophoresis is employed to check the progression of a restriction enzyme digestion. — True. R is about how the digestion is checked. Running a sample on a gel shows whether the DNA has been cut.
Why R does not explain A? R tells us how we follow the digestion after it has started, by running samples on a gel. It says nothing about why the enzyme must be given its optimal conditions; that need comes from the enzyme itself, which works best under particular conditions. Checking a reaction is not the cause of the way the reaction is set up. So both statements are correct, but R is not the explanation of A.
NCERT Extract:
Cutting of DNA at Specific Locations – “Restriction enzyme digestions are performed by incubating purified DNA molecules with the restriction enzyme, at the optimal conditions for that specific enzyme. Agarose gel electrophoresis is employed to check the progression of a restriction enzyme digestion. DNA is a negatively charged molecule, hence it moves towards the positive electrode (anode) (Figure 9.3).”