An activator protein would have which of the following effects on an operon with a positive control mechanism?
a. Stimulate transcription.
b. Turn off transcription.
c. Stimulate transcription when a coactivator is bound to the allosteric site.
d. Inhibit transcription when a coactivator is bound to the allosteric site.
e. Activator proteins only work on operons under negative control.
c
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A compound similar to auxin, 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), has been used
A. as a fertilizer for corn and wheat. B. as a spray to promote flowering of pineapple. C. as an organic substitute for chlorine bleach. D. to detoxify the dangerous poison dioxin. E. an herbicide for killing woody seedlings and dicot weeds.
Leptin is a circulating hormone that is produced by fat cells and plays a role in body metabolism and obesity. It normally binds to receptors in the brain and inhibits appetite. Studies have demonstrated that when obese mice that are leptin deficient are injected with leptin they quickly lose their excess weight. Interestingly, however, many overweight people have high levels of leptin in their bloodstream. Why do you think that the high levels of leptin in obese individuals are insufficient to curb their appetite?
A. In obese people with high levels of leptin, the leptin is a non-functional second messenger. B. The form of leptin released by obese people may lack protein kinase activity. C. Obese people who have high levels of leptin may have a leptin receptor with decreased sensitivity. D. Paracrine signaling may be disrupted in obese people with high levels of leptin.
Why are modern light microscopes better than the ones Leeuwenhoek used?
A. Modern microscopes have a fivefold better resolution. B. Modern microscopes are compound instead of simple. C. Modern microscopes have lenses with smaller numerical apertures. D. Modern lenses are made of prisms. E. Modern microscopes are compound and have five-fold better resolution.
Which sequence lists the layers of a mammalian gut in order, from the outside to the inside (toward the lumen)?
a. mucosa, submucosa, muscularis, serosa b. muscularis, mucosa, submucosa, serosa c. serosa, mucosa, submucosa, muscularis d. serosa, muscularis, submucosa, mucosa