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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.
A series of chemical reactions with each reactant labeled. The first reaction is tyrosine with an arrow pointing to Z-p-hydroxyphenylacetaldoxime. Next to the arrow is the label Enzyme 1. The second reaction is Z-p-hydroxyphenylacetaldoxime with an arrow pointing to p-hydroxymandelonitrile. Next to the arrow is the label Enzyme 2. The third reaction has 2 arrows from p-hydroxymandelonitrile. The first arrow points from p-hydroxymandelonitrile to Dhurrin and next to the arrow is the label Enzyme 3. The second arrow from p-hydroxymandelonitrile points to p-hydroxybenzaldehyde plus hydrogen cyanide.
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?
Choose 1 answer: