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AP®︎/College Biology

Course: AP®︎/College Biology > Unit 3

Lesson 3: Cellular energy

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.

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AP®︎/College Biology

Course: AP®︎/College Biology > Unit 3

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