Answer:
Sleep.
Awaken.
Explanation:
The time and duration of circadian rhythms are regulated by the interactions of PER(period) and TIM(timeless) genes and their proteins. The TIM proteins binds with PER- proteins and the two entered the cell nucleus to set up circadian rhythms.
At midday the two genes becomes active,and their DNAs transcribed to form PER-RNA, and TIM -RNA. These RNAs accumulated in the cell nucleus over some hours.
At dusk(night) the amount of these RNAs reached highest levels.and are translated to the PER and TIM -proteins, which bonded together and moved into the cells nucleus causing sleep in the animals.
Hours to dawn,(morning) the concentration of the two proteins exceeded their limit, and signals is sent to their genes to stop transcription, thus the protein(PER and TIM) synthesis is stopped.
At almost dawn, the PER and TIM proteins disintegrates, the cycle begins again and the individual is awake.
