12. Enzyme-linked immunosorbent assay (ELISA) is used for
(a) Quantifying antibody levels in blood
(b) Determining the molecular weight of an antigen
(c) Purifying proteins from biological fluids
(d) Determining the molecular weight of an antibody
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Enzyme-linked immunosorbent assay, or ELISA, stands as a cornerstone technique in biotechnology, microbiology, and clinical diagnostics. If you’re studying biochemistry or preparing for exams, you might encounter questions like: “ELISA is used for?” This article breaks down a common multiple-choice query, reveals the correct answer with step-by-step reasoning, and explains every option to build your understanding.
The correct answer is (a) Quantifying antibody levels in blood. ELISA excels at detecting and measuring specific proteins, like antibodies, with high sensitivity and specificity. Let’s dive into why.
Correct Answer: Why ELISA Quantifies Antibody Levels
ELISA leverages antigen-antibody interactions in a 96-well plate format. Here’s how it works:
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Capture Phase: A target antigen coats the wells.
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Binding: Patient serum (containing potential antibodies) is added; specific antibodies bind to the antigen.
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Detection: Enzyme-linked secondary antibodies bind to the primary antibodies. Adding a substrate triggers a color change, proportional to antibody concentration.
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Quantification: Absorbance is measured via spectrophotometer, yielding precise levels (e.g., IgG or IgM in blood for disease diagnosis).
This makes ELISA ideal for quantifying antibody levels in blood—think HIV testing, COVID-19 serology, or allergy diagnostics. Studies from sources like the Journal of Immunological Methods confirm its detection range from picograms to micrograms per milliliter, far surpassing qualitative tests.
In your biotech research, ELISA’s versatility shines in microbial assays or enzyme kinetics studies, aligning with fermentation monitoring or vaccine development.
Why Not the Other Options? Detailed Breakdown
Each incorrect option confuses ELISA with other techniques. Here’s a clear comparison:
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(b) Determining the molecular weight of an antigen
Wrong. Molecular weight requires gel electrophoresis (SDS-PAGE) or mass spectrometry, which separate proteins by size or mass-to-charge ratio. ELISA focuses on binding affinity, not size—irrelevant for antigens like viral proteins. -
(c) Purifying proteins from biological fluids
No. Purification uses chromatography (affinity, ion-exchange) or centrifugation. ELISA is analytical, not preparative; it consumes samples without yielding pure proteins. For bioengineers purifying enzymes from fermentation broths, opt for His-tag affinity columns instead. -
(d) Determining the molecular weight of an antibody
Incorrect for the same reason as (b). Antibodies (e.g., IgG at ~150 kDa) need SDS-PAGE or Western blot for size estimation. ELISA ignores molecular weight, prioritizing quantity via colorimetric signals.
| Option | Technique | Purpose | Why Not ELISA? |
|---|---|---|---|
| (a) | ELISA | Quantify antibodies | Correct – Measures concentration via enzyme reaction |
| (b) | SDS-PAGE/Mass Spec | Antigen MW | Binding-based, not size-based |
| (c) | Chromatography | Protein purification | Analytical, not isolation |
| (d) | SDS-PAGE | Antibody MW | No size separation |
Real-World ELISA Applications in Biotech
Beyond exams, ELISA is used for hormone assays, toxin detection in food microbiology, and cytokine profiling in cell culture. In India’s growing biotech sector (e.g., Jaipur’s research hubs), it’s vital for monoclonal antibody production and microbial growth kinetics validation.
Mastering ELISA boosts your skills in molecular biology techniques—perfect for your enzyme kinetics or genetic engineering projects.
