News that the 2017 Nobel Prize for Physiology or Medicine has been shared by 3 American scientists who initially independently attempted to elucidate the molecular mechanism found in the cells of all multicellular organisms that controls the circadian rhythm (https://www.theguardian.com/science/2017/oct/02/nobel-prizes-2017-everything-you-need-to-know-about-circadian-rhythms). Circadian rhythms are, as the name suggests, close to the 24 hours of the day-night cycle imposed on the life forms of our planet by the Earth revolving as it travels around our nearest star. Most life forms are directly or indirectly dependent on solar energy, so it increases biological efficiency if individual cells 'know' (often without direct cues) when it is likely to be light or dark. Studies (largely with the fruit-fly Drosophila) revealed that proteins released from a 'period' gene rise and fall throughout the day in a negative feedback loop (in the same way that a central heating system is controlled- the hotter the room, the less fuel is supplied to the heater). A second gene labelled 'timeless' also produces proteins that combine with those produced by the 'period' gene, facilitating entry to the cell's DNA in its nucleus to 'switch off' the 'period' gene. 'Timeless' essentially controls the periodicity of the biorhythm. Simples.
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