Arrange the steps of gel electrophoresis in a proper sequence:
(A) Fragments of DNA are separated under an electric field in agarose gel
(B) DNA bands are cut out from the agarose gel and extracted
(C) DNA fragments are visualized by exposure to UV radiation
(D) Separated DNA fragment stained with ethidium bromide
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A), (D), (C), (B)
DNA fragments are separated in agarose gel under an electric field (A), stained with ethidium bromide (D) and seen under ultraviolet (UV) light (C); the bands are then cut out and extracted (B), called elution.
NCERT Extract:
Restriction Enzymes – “… Since DNA fragments are negatively charged molecules they can be separated by forcing them to move towards the anode under an electric field through a medium/matrix. 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.”
Restriction Enzymes – “The separated DNA fragments can be visualised only after staining the DNA with a compound known as ethidium bromide followed by exposure to UV radiation (you cannot see pure DNA fragments in the visible light and without staining). You can see bright orange coloured bands of DNA in a ethidium bromide stained gel exposed to UV light (Figure 9.3). The separated bands of DNA are cut out from the agarose gel and extracted from the gel piece. This step is known as elution.”