Q.33

The method(s) used to detect a DNA fragment of 150 base pairs is/are

(A) agarose gel electrophoresis

(B) northern blotting

(C) polyacrylamide gel electrophoresis

(D) western blotting

Detecting 150 bp DNA Fragments: Agarose Gel Electrophoresis Explained

Agarose gel electrophoresis effectively separates and detects DNA fragments around 150 base pairs (bp), making it a standard technique in molecular biology labs. This method leverages size-based migration under an electric field to visualize specific bands.

Correct Answer

The correct options are (A) agarose gel electrophoresis and (C) polyacrylamide gel electrophoresis. Both techniques resolve small DNA fragments like 150 bp through gel matrices, with staining for detection under UV light.

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Agarose Gel Electrophoresis (Option A)

Agarose gel electrophoresis separates DNA from 100 bp to 25 kb by applying an electric field, where negatively charged DNA migrates toward the anode based on size. A 1-2% agarose concentration provides optimal resolution for 150 bp fragments, visualized with ethidium bromide or SYBR dyes. This routine method suits PCR products and restriction digests in research settings.

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Northern Blotting (Option B)

Northern blotting detects RNA molecules, not DNA, by separating RNA via gel electrophoresis, transferring to a membrane, and hybridizing with DNA probes. It targets mRNA expression analysis, rendering it unsuitable for naked DNA fragments like 150 bp.

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Polyacrylamide Gel Electrophoresis (Option C)

Polyacrylamide gel electrophoresis (PAGE) excels at resolving smaller DNA fragments below 1 kb, including 150 bp, due to its finer pore structure compared to agarose. Denaturing PAGE with urea ensures single-stranded DNA separation for precise sizing in sequencing or mutation detection.

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Western Blotting (Option D)

Western blotting identifies proteins via SDS-PAGE separation, membrane transfer, and antibody probing, bypassing DNA entirely. This immunoassay has no role in DNA fragment detection.

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Key Differences in DNA Detection Techniques