The GATE Grind

GATE 2023 BT – Question 23

Plant, Animal and Microbial Biotechnology · Animals: Hybridoma technology, stem cells, animal cloning, transgenic, knock-out and knock-in animals · 1 mark · Multiple choice

In hybridoma technology, which one of the following enzymes is absent in the myeloma cells that are used for monoclonal antibody production?

  1. Hypoxanthine-guanine phosphoribosyltransferase
  2. Alanine aminotransferase
  3. Triose phosphate isomerase
  4. Glycosyltransferase

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Show answer and explanation

Correct answer: (A) Hypoxanthine-guanine phosphoribosyltransferase

Explanation

**Hybridoma technology.** A hybridoma is made by fusing an antibody-producing B cell (which is mortal in culture) with an immortal **myeloma** cell.

**Selection.** The fused cells are grown in **HAT medium** (hypoxanthine, aminopterin, thymidine):
- Aminopterin blocks the *de novo* nucleotide synthesis pathway, so cells must use the **salvage pathway**, which needs the enzyme **HGPRT** (hypoxanthine-guanine phosphoribosyltransferase).
- The myeloma cells used are **HGPRT-deficient**, so unfused myeloma cells die in HAT medium.
- Unfused B cells die naturally because they do not grow in culture.
- Only the hybrids survive: they get HGPRT from the B cell and immortality from the myeloma.

Answer **HGPRT** (A).