Question

The inter-chelating agent used as a stain for visualizing DNA in a UV spectrophotometer is

• A. Ethidium Bromide
• B. Bromophenol
• C. Silver Nitrate
• D. X Gal

Hint:

Ethidium Bromide is a classic planar dye that intercalates between DNA base pairs, absorbing UV light and emitting fluorescent light to make DNA bands visible.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Visualizing nucleic acid fragments after gel electrophoresis requires a fluorescent dye that binds to DNA and fluoresces under ultraviolet (UV) light excitation.

Step 2: Detailed Explanation:
Ethidium Bromide (EtBr) is a flat, planar molecule that acts as an intercalating agent.
Its planar structure allows it to slide between adjacent nitrogenous base pairs of the DNA double helix.
When intercalated within the hydrophobic environment of the DNA stack, the fluorescence yield of Ethidium Bromide increases significantly compared to when it is free in solution.
Upon exposure to UV light, the DNA-bound Ethidium Bromide absorbs light and emits a bright orange-red fluorescence, allowing researchers to visualize and photograph DNA bands on an agarose gel.
Bromophenol blue (B) is a tracking dye used to monitor the progress of electrophoresis, but it does not stain DNA.
Silver nitrate (C) is a highly sensitive non-fluorescent stain used primarily for proteins and small nucleic acid fragments in polyacrylamide gels.
X-gal (D) is a chromogenic substrate used to detect \(\beta\)-galactosidase activity in blue-white colony screening.

Step 3: Final Answer:
Therefore, the intercalating agent used for DNA visualization is Ethidium Bromide, which corresponds to option (A).