Comprehension:
Restriction Enzymes
Read the following passage carefully and answer the given questions.
Genetic engineering is the combination of techniques to alter the chemistry of genetic material (DNA and RNA), to introduce these into host organisms and thus change the phenotype of the host organism. The first restriction endonuclease–Hind II, whose functioning depended on a specific DNA nucleotide sequence was isolated and characterised five years later. It was found that Hind II always cut DNA molecules at a particular point by recognising a specific sequence of six base pairs. This specific base sequence is known as the recognition sequence for Hind II. Besides Hind II, today we know more than 900 restriction enzymes that have been isolated from over 230 strains of bacteria each of which recognise different recognition sequences. Restriction enzymes belong to a larger class of enzymes called nucleases namely exonucleases and endonucleases. The DNA fragments can be separated according to their size through sieving effect by gel electrophoresis. Hence, the smaller the fragment size, the farther it moves.
The fragments of DNA are separated by:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Agarose gel electrophoresis
(1) Agarose gel electrophoresis — Correct. DNA fragments are negatively charged. In gel electrophoresis they are made to move towards the anode under an electric field, through a gel of agarose. The gel acts like a sieve, so the fragments separate according to their size. The smaller the fragment, the farther it moves.
(2) Centrifugation — Incorrect. This method separates particles by their mass and density in a spinning tube. It is not used to sort DNA fragments by length.
(3) PCR — Incorrect. The polymerase chain reaction makes many copies of a piece of DNA. It does not separate fragments.
(4) ELISA — Incorrect. ELISA (enzyme linked immuno-sorbent assay) detects an antigen or an antibody through their reaction. It is not a method for separating DNA.
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) 2026 on 07-06-2026 (Slot 2) and on 14-05-2026 (Slot 1), in CUET (UG) 2025 on 29-05-2025 (Slot 1), and in CUET (UG) 2022 on 23-08-2022 (Slot 3).
NCERT Extract:
Restriction Enzymes – “… Nowadays the most commonly used matrix is agarose which is a natural polymer extracted from sea weeds. The DNA fragments separate (resolve) according to their size through sieving effect provided by the agarose gel. Hence, the smaller the fragment size, the farther it moves.”