8. In terpene biosynthesis pathways, three acetyl-CoA are joined together stepwise to form mevalonic acid. mevalonic acid to form isopentenyl diphosphate or Which one of the following three- steps is required by isopentenyl pyrophosphate (IPP)?
(1)Pyrophosphorylation, decarboxylation, and dehydration.
(2)Alkylation, pyrophosphorylation and decarboxylation.
(3) Methylation, dehydration and alkylation.
(4) Phosphorylation, carboxylation and methylation.
Correct answer: (1) Pyrophosphorylation, decarboxylation, and dehydration.
Explanation:
-
In the biosynthesis of isopentenyl pyrophosphate (IPP) from mevalonic acid, the process includes:
-
Pyrophosphorylation: Addition of phosphate groups converts mevalonic acid into mevalonate-5-pyrophosphate.
-
Decarboxylation: Mevalonate-5-pyrophosphate undergoes decarboxylation, removing CO2.
-
Dehydration: Followed by the removal of water (dehydration) to form isopentenyl pyrophosphate, the key 5-carbon building block in terpene biosynthesis.
-
-
These sequential steps are essential for transforming the initial precursors into the activated IPP needed for terpene formation.
Option-wise:
-
(1) Pyrophosphorylation, decarboxylation, and dehydration — Correct.
-
(2) Alkylation, pyrophosphorylation and decarboxylation — Incorrect sequence and steps.
-
(3) Methylation, dehydration and alkylation — Not involved in IPP formation at this stage.
-
(4) Phosphorylation, carboxylation and methylation — Incorrect; decarboxylation, not carboxylation, occurs.
Isopentenyl pyrophosphate (IPP) formation from mevalonic acid involves pyrophosphorylation to generate mevalonate-5-pyrophosphate, followed by decarboxylation and dehydration steps that produce IPP, the essential isoprene unit for building terpenes in plants.
