Gel Electrophoresis
Read the following passage carefully and answer the questions given below:
As a result of cutting DNA by restriction endonucleases, DNA becomes fragmented. These fragments can be separated by gel electrophoresis. Since DNA fragments are negatively charged, they are made to move towards the anode under an electric field and are separated according to their size. The matrix agarose, which is commonly used nowadays, is a natural polymer extracted from seaweeds. DNA fragments move through the sieving effect of the agarose gel and get separated according to their size. Therefore, the smaller the fragment size, the farther they move. After staining the separated DNA fragments with a compound called ethidium bromide, they can be seen as bright orange coloured bands when exposed to UV radiation. The separated DNA fragments are cut out from the agarose gel and extracted from the gel pieces. This process is called elution. The DNA purified in this way is joined to cloning vectors for the construction of recombinant DNA.
In gel electrophoresis, DNA fragments move towards the __________.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Anode
DNA carries negative charge because of the phosphate groups in its backbone. In gel electrophoresis an electric field is applied across the gel. Opposite charges attract, so the negatively charged DNA fragments move towards the positive electrode, the anode.
(1) Cathode — Incorrect. The cathode is the negative electrode. It repels the negatively charged DNA.
(2) Anode — Correct. DNA moves towards the positive anode.
(3) Electrolyte — Incorrect. An electrolyte is a solution that carries the current. It is not an electrode, so DNA does not move towards it.
(4) Buffer — Incorrect. The buffer keeps the pH steady and carries the current. It is not the place the DNA moves to.
Note 1: 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.
Note 2: A similar question was also asked in CUET (UG) 2025 on 20-05-2025 (Slot 2).