Watch the video at http://www.hhmi.org/biointeractive/drosophila-molecular-clock
ID: 60770 • Letter: W
Question
Watch the video at http://www.hhmi.org/biointeractive/drosophila-molecular-clock-model
The video presents several of the molecular participants in the biological clock mechanisms of fruit flies.
Summarize the circadian (at dawn, noon, sunset, and midnight) changes (increasing, decreasing or steady) in ONE of the following sets:
1) per mRNA, PER protein, tim mRNA, TIM protein, PER-TIM heterodimer
2) cyc mRNA, CYCLE protein, clk mRNA, CLOCK protein, CLK-CYC heterodimer
including CRYPTOCHROME and DOUBLETIME KINASE in your answer.
Explanation / Answer
1)-
In absence of light, PER & TIM are both formed from the respective mRNAs. In presence of increased concentration of PER & TIM, PER-TIM heterodimers are formed. These heterodimers accumulate & around midnight, when enough have been formed, they enter the nucleus & inactivate the transcription factors CYC-CLK; & hence prevent transcription of per & tim mRNAS & therefore the respective proteins.
At dawn, in presence of light, CRY is activated & it inactivates TIM protein- as a result, PER-TIM heterodimer is destroyed & then PER is being inactivated by DOUBLE-TIME KINASE. This allows CYC-CLK to again bind to promoters of per & tim genes & start transcription & eventually translation.
ELEMENTS controlling circadian rhythm
DAWN
NOON
SUNSET
MIDNIGHT
per mRNA
Begins increasing
increasing
steady
decreasing
PER protein
steady
decreasing
increasing
steady
tim mRNA
Begins increasing
increasing
steady
decreasing
TIM protein
Begins decreasing due to activation of CRY protein
decreasing
increasing
steady
PER-TIM heterodimer
Begins decreasing
decreasing
increasing
steady
ELEMENTS controlling circadian rhythm
DAWN
NOON
SUNSET
MIDNIGHT
per mRNA
Begins increasing
increasing
steady
decreasing
PER protein
steady
decreasing
increasing
steady
tim mRNA
Begins increasing
increasing
steady
decreasing
TIM protein
Begins decreasing due to activation of CRY protein
decreasing
increasing
steady
PER-TIM heterodimer
Begins decreasing
decreasing
increasing
steady
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