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Cellular energy

The plant Sorghum bicolor produces an anti-herbivory chemical called dhurrin. Dhurrin is synthesized from the amino acid tyrosine in a three-step metabolic pathway.

Each step in the dhurrin biosynthesis pathway is catalyzed by a different enzyme. Dhurrin, the final product, can be stored safely in the cell. However, a molecule produced from the reaction catalyzed by Enzyme 2 can be immediately metabolized to form hydrogen cyanide, which is a toxic substance.

These pathways are summarized in the following diagram.

Arabidopsis thaliana is a plant species that doesn’t normally synthesize dhurrin. In an experiment, a team of scientists engineered a group of A. thaliana plants to make Enzymes 1, 2, and 3 from S. bicolor in different combinations. A. thaliana plants that made just Enzymes 1 and 2 did not produce dhurrin and were stunted in growth. A. thaliana plants that made Enzymes 1, 2, and 3 produced dhurrin and grew normally.

Which of the following claims is best supported by the experimental results described above?

(Choice A)
Non-engineered A. thaliana plants do not contain the reactant required by Enzyme 1.
(Choice B)
The product of the reaction catalyzed by Enzyme 3 is toxic to A. thaliana plants, causing stunted growth.
(Choice C)
The product of the reaction catalyzed by Enzyme 2 is efficiently transferred to Enzyme 3.
(Choice D)
Non-engineered A. thaliana plants make an enzyme that functions similarly to Enzyme 3 from S. bicolor.

Jørgensen, Kirsten, Anne V. Rasmussen, Marc Morant, Allan H. Nielsen, Nanna Bjarnholt, Mika Zagrobelny, Søren Bak, and Birger L. Møller. 2005. "Metabolon formation and metabolic channeling in the biosynthesis of plant natural products." Current Opinion in Plant Biology 8(3): 280–91. doi:10.1016/j.pbi.2005.03.014

Kristensen, Charlotte, Marc Morant, Carl Erik Olsen, Claus T. Ekstrøm, David W. Galbraith, Birger L. Møller, and Søren Bak. 2005. "Metabolic engineering of dhurrin in transgenic Arabidopsis plants with marginal inadvertent effects on the metabolome and transcriptome." Proceedings of the National Academy of Sciences of the USA 102(5):1779–84. doi:10.1073/pnas.0409233102

Biology library

Course: Biology library > Unit 21

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