Gel electrophoresis
Read the following passage carefully and answer the given questions.
The cutting of DNA by molecular scissors results in 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 electrode under an electric field through a matrix. Nowadays, most commonly used matrix is agarose, which is a natural polymer. The DNA fragments resolve according to their size through sieving effect provided by agarose gel. Hence, smaller fragment size, farther it moves. The separated DNA fragments can be visualized only after staining DNA with a dye followed by exposure to radiation. The separated bands of DNA are cut out from agarose gel and extracted from gel piece. The DNA fragments purified in this way are used in construction recombinant DNA by joining them with cloning vectors.
Separated DNA bands in agarose gel can be extracted by the process of:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Elution
After electrophoresis, the bands of DNA are cut out from the agarose gel. The DNA is then taken out of the gel piece. This step is called elution. The DNA fragments purified in this way are used to build recombinant DNA by joining them with cloning vectors.
(1) Ligation — Incorrect. This is the joining of DNA fragments with the enzyme DNA ligase. It comes later, when the fragment is linked to a vector.
(2) Centrifugation — Incorrect. It separates materials by spinning them. It is not the name of this step.
(3) Elution — Correct. It means taking the DNA out of the gel piece.
(4) Staining — Incorrect. Staining only makes the DNA visible. It comes before the bands are cut out.
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 – …
