![]() ![]() Eventually levels of those proteins reach a certain threshold they then shut off creation of the messenger RNA that produces them. At particular times of day, certain clock proteins switch on production of messenger RNA, used by the cell to bake fresh batches of other clock proteins. They’re composed of RNA molecules and proteins that oscillate in abundance. The ancestral clock may have started out as simple as a sundial, researchers say, but it provided a foundation for building the more elaborate mechanisms that now control everything from blood pressure to bedtime.Ĭircadian clocks don’t have gears and hands. The original biological timepiece may not have resembled the precision body clocks that scientists study today. This clock helps algae synchronize photosynthesis with sunlight. At night, KaiB blocks KaiA and the phosphates are stripped from KaiC by dawn. KaiA helps KaiC add phosphate (purple) to itself by dusk. Blue-green algae have one of the simplest circadian clocks, with three protein gears. That clock evolved to shield the cell from oxygen damage or perhaps provide other, unknown advantages. They say there had to be one mother clock from which all others came. ![]() But a small group of researchers think otherwise. Creatures probably did this to protect their fragile DNA from the sun’s damaging ultraviolet rays. Many scientists favor the view that multiple organisms independently evolved their own circadian clocks, each reinventing its own wheel. ![]() But as common and important as circadian clocks have become, exactly why such timepieces arose in the first place has been a deep and abiding mystery. Having timekeepers offers such an evolutionary advantage that species have developed them again and again throughout history, many scientists say. ![]()
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