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GATE 2020 BT Q.6: solution and answer

GATE 2020 · BTQ.6 · 1 mark · MCQ

Vincristine and vinblastine, two commercially important secondary metabolites from Catharanthus roseus, are examples of

  1. (A)

    alkaloids.

  2. (B)

    flavonoids.

  3. (C)

    terpenoids.

  4. (D)

    steroids.

See the question in the paper
GATE 2020 BT question 6Tap to open full size

Answer and solution

ANSWER

Vincristine and vinblastine are indole alkaloids, so the answer is (A) alkaloids.

Official answer: ASource: Official answer key, GATE 2020 BT (IIT Delhi)

  1. Vincristine and vinblastine are the vinca anticancer drugs of Madagascar periwinkle, Catharanthus roseus. Each is a dimer of two monoterpenoid indole alkaloid units, catharanthine and vindoline.

  2. Both units are built from tryptophan (via tryptamine) joined to the terpenoid-iridoid secologanin by strictosidine synthase. The products are nitrogen-containing, basic, plant-derived compounds, which is the definition of an alkaloid.

  3. (A) alkaloids: correct. Both compounds are indole alkaloids, and they are the standard example of alkaloids obtained from plant cell and tissue culture.

  4. (B) flavonoids: wrong. Flavonoids are phenylpropanoid-derived polyphenols with a skeleton (for example quercetin) and contain no indole ring.

  5. (C) terpenoids: wrong as the best answer. Secologanin contributes a terpenoid-derived part, but the final molecules are classified by their nitrogen-containing indole core as alkaloids. Typical terpenoids are taxol and artemisinin.

  6. (D) steroids: wrong. Steroids have the four-ring cyclopentanoperhydrophenanthrene nucleus derived from squalene (for example diosgenin), unrelated to the dimeric indole structure.

  7. So the answer is (A).

KEY IDEA

Classify a natural product by its core structure and biosynthetic class. Vinca compounds contain nitrogen in an indole ring, made from tryptophan plus a terpenoid unit, so they are monoterpenoid indole alkaloids.

WATCH OUT FOR

Choosing terpenoids because the secologanin part comes from the terpenoid pathway. Mixed-origin compounds are named by their nitrogenous core, so these are alkaloids. Paclitaxel (taxol) is the standard terpenoid anticancer example.

From the GATE 2020 BT paper. Every question of this paper · Download the full paper · All 8 Plant tissue culture questions, with notes

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