Subtopic: Fundamentals of Downstream processing (chromatography, filtration)
Question Statement:
Enzyme-linked immunosorbent assay (ELISA) is used for
Options:
(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
Official Answer Key:
A
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE BT 2017 Q.12)**
**1. Governing Concept & Question Classification**:
- **Section**: BT
- **Question Type**: **MCQ** (1 Mark)
- **Topic**: Immunology & Bioanalytical Techniques (ELISA Applications)
**2. Detailed Step-by-Step Analysis**:
- **Enzyme-Linked Immunosorbent Assay (ELISA)** is an immunological assay that utilizes an immobilized antigen or antibody to specifically capture its cognate binding partner from a solution, followed by signal generation using an enzyme-conjugated secondary antibody (e.g., Horseradish Peroxidase, HRP, or Alkaline Phosphatase, AP) that converts a chromogenic substrate into a detectable colored or fluorescent product.
- By comparing optical absorbance against a standard calibration curve, ELISA provides sensitive **quantification of antibody or antigen titers/levels** in complex biological fluids such as serum, plasma, and blood.
- ELISA does not separate molecules by molecular weight or mass; molecular weights are determined by SDS-PAGE, mass spectrometry (MALDI-TOF), or analytical ultracentrifugation.
- **Option-by-Option Evaluation**:
- **Option (A) [CORRECT]**: ELISA is a standard, highly sensitive method for quantifying antibody (or antigen) concentrations in blood/serum.
- **Option (B) [INCORRECT]**: Molecular weight determination requires gel electrophoresis or mass spectrometry, not ELISA.
- **Option (C) [INCORRECT]**: Preparative protein purification is performed using chromatography (e.g., affinity, ion exchange), not analytical ELISA.
- **Option (D) [INCORRECT]**: ELISA cannot determine the molecular weight of an antibody.
**3. Final Answer / Verification Summary**:
- **Official GATE Answer Key**: **A**
- **Scoring Criteria**: +1.0 Mark (Negative marking: -0.33 marks).
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