9. The gene encoding for mevalonate-3-kinase is disrupted in a certain plant. Which one of the following staternents concerning the above plant is correct?
(1) Mevalonic acid 3,5-biphosPhate will be synthesized, while there will be no synthesis of Mevalonic acid 5-phosphate.
(2) Mevalonic acid 3,5-biphosphate and Isopentenyl diphosphate will be synthesized.
(3) There will be no synthesis of Mevalonic acid 3, 5- biphosphate but Mevalonic acid will be synthesized.
(4) Aceto acetyle-coA and Mevalonic acid will not be synthesized.
Correct answer: (3) There will be no synthesis of Mevalonic acid 3,5-biphosphate but Mevalonic acid will be synthesized.
Explanation:
-
Mevalonate-3-kinase catalyzes the phosphorylation of mevalonic acid at the 3-position, producing mevalonate-3-phosphate and downstream products such as mevalonate-3,5-bisphosphate.
-
Disruption of mevalonate-3-kinase gene implies mevalonate cannot be phosphorylated at the 3-position, therefore no synthesis of mevalonate-3,5-bisphosphate.
-
However, mevalonate itself is still synthesized upstream from acetoacetyl-CoA and HMG-CoA, so mevalonate production occurs normally.
-
Since phosphorylation at 5-position (mevalonate-5-phosphate) occurs via different kinases, its synthesis might still proceed independently, but disruption of 3-kinase specifically affects 3-phosphorylation steps.
-
Also, acetoacetyl-CoA and mevalonate are synthesized upstream, so statement (4) is incorrect.
Option analysis:
-
(1) Incorrect; no mevalonate-3,5-bisphosphate synthesized if 3-kinase is disrupted.
-
(2) Incorrect; mevalonate-3,5-biphosphate synthesis blocked, so IPP from that route blocked.
-
(3) Correct; no mevalonate-3,5-bisphosphate, but mevalonate synthesis normal.
-
(4) Incorrect; acetoacetyl-CoA and mevalonate are synthesized normally upstream.
Disruption of mevalonate-3-kinase halts phosphorylation of mevalonate at the 3-position, preventing mevalonate-3,5-bisphosphate formation, though mevalonate itself is still produced from acetoacetyl-CoA and HMG-CoA, affecting downstream isoprenoid biosynthesis pathways.
