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, the process of elution is:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Separated bands of DNA are cut out from the agarose gel and extracted.
Elution is the step that follows gel electrophoresis. The separated bands of DNA are cut out from the agarose gel and the DNA is extracted from the gel pieces. The DNA purified in this way is then joined to a cloning vector to make recombinant DNA.
(1) Separated bands of enzymes are cut out from the agarose gel and extracted. — Incorrect. The bands on the gel are DNA fragments, not enzymes.
(2) Separated bands of proteins are cut out from the agarose gel and extracted. — Incorrect. Proteins are not what is separated here. The method separates DNA fragments.
(3) Separated bands of DNA are cut out from the agarose gel and extracted. — Correct. This is elution.
(4) Separated bands of RNA are cut out from the agarose gel and extracted. — Incorrect. The fragments come from DNA cut by restriction enzymes, not from RNA.
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.