Circadian rhythm is name given to the “internal body clock” that regulates the (roughly) 24 hour cycle of biological processes in animals and plants. Circadian rhythms are important in determining the sleeping and feeding patterns of all animals, including humans. There are clear patterns of brain wave activity, hormone production, cell regeneration and other biological activities linked to this 24 hour cycle.
Exactly how and when life began keeping time is unclear, but a candidate for the original biological clock may solve the mystery.
Biological clocks are ubiquitous in nature, so the first clock should pre-date the evolutionary parting of the ways that led to modern groups of organisms. All the clocks found so far are unique to different groups of organisms, though. Not so the clock discovered recently by scientists. In an enzyme called peroxiredoxin (PRX), they seem to have found a grandfather clock – one that is common to nearly all life.
PRX gets rid of poisonous, highly reactive oxygen (ROS), which is produced by oxygen-based metabolism. And the enzyme oscillates: it flits between an active and inactive state, depending on whether oxygen is bound to the active site. Using antibodies that bind only to the oxidised enzyme, the team found that PRX oxidation keeps cycling independently on a 24-hour cycle, even when organisms were kept in constant light or constant dark. Learn more here or here.