Question

glucose
sterol
after the incubation period, the researchers identified three types of sterols in each of the t. brucei samples. they then determined the percent of each type of sterol that contained the radiolabeled carbon. the table below shows these results.

type of sterol	normal glucose medium	radiolabeled glucose medium
cholestatrienol	1.25%	7.0%
ergosterol	1.00%	4.0%

data adapted from millerioux et al. 2018. plos pathogens. licensed under cc by 4.0.

based on this information, which of the following best predicts the effect of a decrease in glucose in the environment of t. brucei?

a. an increase in sterol synthesis, since the cells will have access to more oxygen atoms to incorporate into sterols
b. an increase in glucose synthesis, since the cells can produce the sugar molecules needed to make lipids
c. no change in sterol synthesis, since the cells do not need to uptake glucose from their environment to produce lipids
d. a decrease in sterol synthesis, since the cells will be deficient in the hydrocarbon backbones provided by sugar molecules

Explanation:

1. Analyze the table: In radiolabeled glucose medium, the percent of sterol with \(^{14}\text{C}\) (from glucose) is higher than in normal glucose medium. This shows glucose is used in sterol synthesis.
2. Evaluate Option A: Oxygen atoms aren't the main source for sterol carbon backbones (glucose provides carbon). So A is incorrect.
3. Evaluate Option B: The question is about glucose decrease's effect on sterol synthesis, not glucose synthesis. B is irrelevant.
4. Evaluate Option C: The table shows glucose is used for sterol synthesis, so a glucose decrease should affect it. C is incorrect.
5. Evaluate Option D: Glucose (a sugar) provides hydrocarbon backbones (carbon chains) for sterol synthesis. A glucose decrease would limit these backbones, reducing sterol synthesis. D matches the logic.

Answer:

D. a decrease in sterol synthesis, since the cells will be deficient in the hydrocarbon backbones provided by sugar molecules