Circadian Rhythms

Abstract Daily (circadian) rhythms of behaviour and physiology are prevalent in organisms ranging from cyanobacteria to humans. These rhythms are not simply responses to environmental cues, but are driven by endogenous cellular clocks. Circadian clocks are synchronised to daily environmental cycles to produce 24 h molecular oscillations, which in turn drive rhythmic outputs. The mechanisms that produce circadian rhythms have been elucidated in a number of species, and several features of this system are common to most or all rhythmic organisms. Among animals, the molecular components that make up the circadian clock system are highly conserved, and mutations in human clock genes are associated with specific sleep disorders. Circadian rhythms defects in humans are also associated with other serious conditions such as mental health conditions and metabolic disorders. Key Concepts: Circadian rhythms are found in a wide range of organisms. Circadian clocks utilise transcriptional feedback loops and post‐translational modifications. Circadian clocks are located in most or all tissues in humans. Circadian clocks control cell function and physiology through rhythmic gene expression.