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.
Ethidium bromide stains:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → DNA
After gel electrophoresis the DNA fragments cannot be seen, because DNA is colourless. The gel is stained with a compound called ethidium bromide, which binds to the DNA. When the gel is exposed to UV light, the DNA fragments show up as bright orange bands.
(1) Carbohydrates — Incorrect. Ethidium bromide does not stain carbohydrates. Only DNA is separated and stained in this method.
(2) DNA — Correct. Ethidium bromide stains the separated DNA fragments.
(3) Protein — Incorrect. Ethidium bromide is a stain for DNA, not for proteins.
(4) Fat — Incorrect. Fats are not separated or stained in this method.
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.