Q.10 Which of the is not a fluorescence
I. Alexa Fluor
2. Green fluorescent protein (GFP)
3. Red fluorescent protein (DsRed)
4. Xylene cyanol
Xylene cyanol is not a fluorescent molecule; it’s a tracking dye used in gel electrophoresis. Options 1-3 are established fluorescent probes widely used in biological imaging and research.
Fluorescence Basics
Fluorescence involves absorbing light at one wavelength and emitting at a longer one, enabling visualization in microscopy and assays. Alexa Fluor dyes, GFP, and DsRed exhibit this property for tagging proteins or cells. Xylene cyanol, however, absorbs visible light to stain gels blue but lacks emission capability.
Option Breakdown
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Alexa Fluor (1): Synthetic dyes with bright, photostable fluorescence across spectra (e.g., 488 nm green); used in labeling antibodies and nucleic acids.
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GFP (2): Naturally fluorescent protein from jellyfish; emits green light (~509 nm) when excited; cornerstone of live-cell imaging.
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DsRed (3): Red fluorescent protein from Discosoma coral (~583 nm emission); enables multi-color labeling with GFP.
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Xylene cyanol (4): Non-fluorescent triarylmethane dye; tracks DNA/RNA migration in agarose gels by color, not emission. Correct non-fluorescent choice.
Fluorescence dyes and proteins like Alexa Fluor, GFP, and DsRed revolutionized molecular biology imaging, but Xylene cyanol stands out as the non-fluorescent option. This which of the following is not a fluorescence analysis targets GATE Life Sciences students seeking precise fluorescence vs tracking dye distinctions.
Key Properties
Alexa Fluor dyes offer superior photostability over FITC, with excitation/emission pairs like 488/519 nm for green fluorescence. GFP autocatalyzes chromophore formation for ~395/509 nm emission, ideal for fusions in vivo. DsRed provides red-shifted fluorescence (~558/583 nm), minimizing GFP overlap in FRET studies. Xylene cyanol, conversely, is a pH-sensitive dye migrating like 100-400 bp DNA in gels without fluorescent emission.
Why Xylene Cyanol?
It absorbs blue light (~610 nm) for visibility but emits none, unlike true fluorophores. In gels, it avoids interfering with actual fluorescent bands (e.g., SYBR-safe DNA stains). Other options are staples in confocal microscopy and flow cytometry.
Exam Strategy
For fluorescence MCQs, recall: synthetic dyes (Alexa), natural proteins (GFP/DsRed) fluoresce; electrophoresis trackers (xylene cyanol, bromophenol blue) do not. Practice with spectra tables and gel images for PYQs.
