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GATE 2023 BT Q.22: solution and answer

GATE 2023 · BTQ.22 · 1 mark · MCQ

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. (A)

    P and R

  2. (B)

    P and Q

  3. (C)

    Q and S

  4. (D)

    R and S

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Answer and solution

ANSWER

The correct answer is (A) P and R — Alkaline phosphatase and Horseradish peroxidase are the enzymes conjugated to antibodies in ELISA for signal detection.

Official answer: ASource: Official answer key, GATE 2023 BT (IIT Kanpur)

  1. The question asks which enzymes, when conjugated to antibodies in ELISA, produce a detectable signal for the analyte.

  2. P. Alkaline phosphatase (ALP) — a standard ELISA reporter enzyme; hydrolyzes chromogenic substrates such as p-nitrophenyl phosphate (pNPP) to give a measurable yellow product. Qualifies.

  3. Q. Trypsinase (trypsin) — a serine protease used for proteolytic digestion/cell dissociation; it has no chromogenic substrate reaction used for ELISA signal readout. Does not qualify.

  4. R. Horseradish peroxidase (HRP) — the other standard ELISA reporter enzyme; oxidizes substrates such as TMB or ABTS in an H2O2-dependent reaction to give a colored, highly sensitive signal. Qualifies.

  5. S. Amylase — hydrolyzes starch; used in digestion/starch assays, not as an antibody-conjugated reporter in immunoassays. Does not qualify.

  6. Only P (alkaline phosphatase) and R (horseradish peroxidase) are genuine ELISA reporter enzymes with established substrate-based detection chemistry.

  7. This corresponds to option (A): P and R.

KEY IDEA

ELISA detection relies on antibody-enzyme conjugates whose enzyme activity produces a measurable colored/chemiluminescent signal upon substrate addition; only alkaline phosphatase and horseradish peroxidase are standard ELISA reporter enzymes among the four listed.

WATCH OUT FOR

Confusing any hydrolytic/digestive enzyme (trypsin, amylase) with a chromogenic reporter enzyme; only enzymes with a colorimetric/chemiluminescent substrate reaction (ALP, HRP) are used as ELISA labels.

From the GATE 2023 BT paper. Every question of this paper · Download the full paper · All 9 Assays & electrophoresis questions, with notes

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