The PER and TIM proteins accumulate during the day until they cause sleepiness. What prevents them from continuing to accumulate at night?
A) Metabolic rates increase at night, so proteins are digested faster than they can be synthesized.
B) The high levels of melatonin present at night react with the proteins to disable them.
C) The proteins are unstable at the lower body temperatures that are typical at night.
D) When the proteins reach a high level, they turn off the genes that produce them.

Question

Quizplus · Accepted Answer

When the PER and TIM proteins reach a high level, they activate their own genes, which produce a protein called PERIOD. The PERIOD protein then inhibits the expression of the PER and TIM genes, preventing further accumulation of these proteins. This creates a negative feedback loop that regulates the circadian rhythm.

The PER and TIM Proteins Accumulate During the Day Until