11. Plants are known to synthesize more than 30,000 terpenoids, involving four stages of biosynthesis.
Column X Column Y
A. Biosynthesis i. Terpene
of two basic five synthases
carbon unit ii. P450
B. Repetitive monooxygenases
addition of C5
units
C. Formation iii. HMG-COA
of the basic synthase
terpenoid
skeletons
D. Modification iv. Prenyltransferases
of terpenoid
skeletons
(1) A-i, B-iii, C-iv, D-ii
(2) A-ii, B-iii, C-i, D-iv
(3) A-i, B-ii, C-iii, D-iv
(4) A-iii, B-iv, C-i, D-ii
Correct answer: (4) A-iii, B-iv, C-i, D-ii
Explanation:
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(A) Biosynthesis of two basic five-carbon units involves the HMG-CoA synthase enzyme in the mevalonate pathway producing the precursor isopentenyl diphosphate (C5 unit).
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(B) Repetitive addition of C5 units to build larger terpenoid chains is carried out by prenyltransferases which link these basic isoprene units.
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(C) Formation of the basic terpenoid skeletons is catalyzed by terpene synthases, enzymes that cyclize or polymerize the prenyltransferase products into diverse skeletons.
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(D) Modification of the terpenoid skeletons by enzymes such as P450 monooxygenases introduces functional groups, oxidation, and structural diversity.
Option-wise:
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(1) A-i, B-iii, C-iv, D-ii — incorrect associations.
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(2) A-ii, B-iii, C-i, D-iv — incorrect associations.
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(3) A-i, B-ii, C-iii, D-iv — incorrect associations.
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(4) A-iii, B-iv, C-i, D-ii — correct.
Plant terpenoid biosynthesis proceeds through four stages: formation of basic five-carbon units by HMG-CoA synthase, chain elongation by prenyltransferases, cyclization by terpene synthases, and functional modification by P450 monooxygenases, each stage catalyzed by specific enzymes generating vast chemical diversity.
1 Comment
Sakshi Kanwar
November 30, 2025A-iii, B-iv, C-i, D-ii