Which of the following is TRUE for gel electrophoresis ?
(A) It is used to separate DNA fragments.
(B) Separation of DNA occurs on the basis of the fragment size.
(C) Separation of DNA fragments occurs on the basis of charge.
(D) Separated DNA fragments can be visualised without staining.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A) and (B) Only
(A) It is used to separate DNA fragments. — True.
(B) Separation of DNA occurs on the basis of the fragment size. — True.
(C) Separation of DNA fragments occurs on the basis of charge. — False. All fragments are negatively charged; they separate by size.
(D) Separated DNA fragments can be visualised without staining. — False. They are seen only after staining with ethidium bromide under UV light.
NCERT Extract:
Restriction Enzymes – “… Separation and isolation of DNA fragments : The cutting of DNA by restriction endonucleases results in the 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 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. … 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.”
