Separation and isolation of DNA fragments
Read the following passage carefully and answer the given questions.
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 toward the electrode under an electric field through a medium. Nowadays, the most commonly used matrix is agarose, a natural polymer extracted from sea weeds. The DNA fragments separate through sieving effect provided by the agarose gel. The separated DNA fragments can be visualised only after staining the DNA with an appropriate dye followed by exposure to UV radiation. The separated bands of DNA are cut out from the agarose gel and extracted from the gel piece. The DNA fragments purified in this way are used in constructing recombinant DNA by joining them with cloning vectors.
In gel electrophoresis, DNA fragments move toward the anode due to:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Negative charge
In gel electrophoresis an electric field is applied across the gel. DNA fragments carry a negative charge because of their phosphate groups, so they move towards the positive electrode, the anode. Opposite charges attract.
(1) Neutral charge — Incorrect. A neutral molecule would not be pulled towards either electrode.
(2) Positive charge — Incorrect. A positively charged molecule would move towards the negative electrode, the cathode.
(3) Negative charge — Correct. This is why the DNA moves towards the anode.
(4) Small and large size of DNA — Incorrect. The size of the fragment decides how far it moves through the gel, because the gel acts as a sieve. The smaller the fragment, the farther it moves. The size does not decide the direction.
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.
NCERT Extract:
Restriction Enzymes – …
