The GATE Grind

GATE 2023 BT – Question 22

Recombinant DNA Technology and Other Tools in Biotechnology · Analytical tools: Electrophoresis, microarrays, enzymatic assays, immunoassays, immunoblotting, flow cytometry, whole genome and ChIP sequencing · 1 mark · Multiple choice

In ELISA, which of the following enzymes are conjugated to antibodies for detection of the analyte? P. Alkaline phosphatase Q. Trypsinase R. Horseradish peroxidase S. Amylase

  1. P and R
  2. P and Q
  3. Q and S
  4. R and S

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Show answer and explanation

Correct answer: (A) P and R

Explanation

In ELISA the detection antibody is linked to an **enzyme** that converts a colourless substrate into a coloured, fluorescent or luminescent product, so the amount of bound analyte can be read out.

The standard enzyme labels are:
- **Alkaline phosphatase (P)** (substrate: p-nitrophenyl phosphate, giving yellow product)
- **Horseradish peroxidase (R)** (substrate: TMB or OPD)

Trypsin(ase) is a protease and amylase digests starch. They are not used as reporter labels in ELISA.

Answer **P and R** (A).