Given below are two statements; one is labelled as assertion A and other is labelled as Reason R
Assertion A: In gel-electrophoresis, DNA fragments are separated.
Reason R: DNA is negatively charged, so it moves towards the cathode under the influence of electric field.
In the light of the above sentences, choose the correct answer from the options given below
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A is true but R is false
Assertion A: In gel-electrophoresis, DNA fragments are separated. — True. Gel electrophoresis separates the DNA fragments made by restriction enzymes. The agarose gel acts like a sieve, so smaller fragments move farther.
Reason R: DNA is negatively charged, so it moves towards the cathode under the influence of electric field. — False. DNA is negatively charged, but a negative charge is pulled to the positive electrode, the anode, not to the cathode.
NCERT Extract:
Restriction Enzymes – “… Separation and isolation of DNA fragments : The cutting of DNA by restriction endonucleases results in the fragments of DNA. These fragments can be separated by a technique known as gel electrophoresis. Since DNA fragments are negatively charged molecules they can be separated by forcing them to move towards the anode under an electric field through a medium/matrix. Nowadays the most commonly used matrix is agarose which is a natural polymer extracted from sea weeds. The DNA fragments separate (resolve) according to their size through sieving effect provided by the agarose gel. Hence, the smaller the fragment size, the farther it moves.”