The stain used to visualize separated DNA by gel electrophoresis is?

KPSC Staff Nurse - 2016

Biochemistry & Nutrition

Easy

Appeared in: KPSC Staff Nurse - 2016

Explanation

Ethidium bromide (EtBr) is a fluorescent dye specifically used to visualize nucleic acids (DNA and RNA) in molecular biology.
It functions as an intercalating agent, meaning it inserts itself between the stacked base pairs of the DNA double helix.
When the gel is placed under an ultraviolet (UV) light source, the DNA-bound EtBr absorbs the UV energy and re-emits it as visible light, fluorescing with a characteristic bright orange-red color.
This fluorescence allows for the easy detection of DNA bands, even in very small quantities (nanograms).

Option B: Haematoxylin is a common stain used in histology, not molecular biology gels. It stains the cell nucleus blue-purple and is typically used with eosin (H&E stain) to examine tissue morphology.
Option C: Acetocarmine is a stain used in cytology, primarily for visualizing chromosomes in preparations like a chromosome squash. It is not used for staining DNA separated by size in a gel matrix.
Option D: Feulgen dye is used in a specific histochemical reaction (the Feulgen reaction) to stain DNA within tissue sections. This method is quantitative and used to measure the amount of DNA in cell nuclei, not for visualizing bands in a gel.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain DNA visualization techniques in gel electrophoresis as background academic context rather than a clinical decision trigger.
Gel electrophoresis is a cornerstone of modern clinical diagnostics. It is used for DNA fingerprinting in forensics, paternity testing, and diagnosing genetic disorders (e.g., sickle cell anemia, cystic fibrosis).
Accurate visualization of DNA bands is critical for interpreting the results of these tests. A faint or unclear band could lead to a misdiagnosis.
Due to the mutagenic nature of Ethidium bromide, many clinical and research labs are now switching to safer, non-mutagenic alternatives like SYBR Safe or GelRed, which also fluoresce but pose a lower health risk.

How to Approach the Question

This is a factual recall question testing knowledge of a standard laboratory technique.
First, identify the key components of the question: the technique ('gel electrophoresis'), the molecule being analyzed ('DNA'), and the purpose ('visualize').
Next, systematically evaluate each option based on its known application in a laboratory setting.
Recall or deduce that Haematoxylin, Acetocarmine, and Feulgen dye are all primarily used in histology or cytology for examining whole cells or tissues under a microscope.
Recognize that Ethidium bromide is the classic fluorescent dye used specifically for making nucleic acids visible in gels.
Conclude that Ethidium bromide is the only option that fits the context of visualizing DNA bands after gel electrophoresis.

Concept Tested & Keywords

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E6 Pathology-Textbook of PATHOLOGYHarsh Mohan Part 1 (1-214) p. 28-30

E6 Pathology-Vandana Puri & Kavita Gaur Textbook of Pathology and Genetics p. 35-37