Molecular Mechanisms in the Circadian Rhythm

Abstract

Circadian clocks evolved to allow organisms to anticipate and adjust their behaviours to the daily change in the external environment. The molecular mechanisms for generating the autonomous oscillation in the circadian clock with a period of ∼24 h, which is named as the transcriptional translational feedback loop (TTFL) model, have been established in the fruit fly Drosophila and are remarkably similar in mammals. The essence of the TTFL is a negative feedback loop with delay: transcription of the clock genes is inhibited by their own gene products (clock proteins). In mammals, circadian rhythms are orchestrated by the central circadian clock in the hypothalamic suprachiasmatic nucleus (SCN), which receives circadian light inputs from the retina. Light, as well as nonphotic inputs, can alter transcription of clock genes in the SCN and entrain the SCN to organise animal physiology and behaviours to be in sync with the environment. Key Concepts Circadian clocks allow organisms to anticipate the daily changing environment. The free‐running period of circadian clocks in constant conditions is close to but not exactly 24 h. The first clock gene was identified in 1984 by the three 2017 Nobel Laureates for Physiology or Medicine. The autonomous oscillation in circadian clocks arises from ∼24 h oscillation of clock genes and clock proteins. In circadian clocks transcription of the clock genes is inhibited by their own gene products (clock proteins). The transcriptional translational feedback loop (TTFL) model is the dominant theory explaining the molecular mechanisms for the circadian clocks. The molecular mechanisms for circadian clocks are very similar in fly and mammals. The hypothalamic suprachiasmatic nucleus (SCN) is the central circadian clock in mammals. Light at night alters expression of clock genes in the SCN and entrains the SCN to synchronise animal behaviours. Circadian disruption in humans is associated with many diseases such as cardiovascular diseases and metabolic disorders.

Disturbance in Chrononutrition and Its Influence on Body Weight and Academic Performance: A Review

“…Molecular mechanism is a transcriptional-translational feedback loop, which is autoregulated. This means that transcription of clock CIM genes is regulated by their protein products [5,6]. Due to modernization, increased work hours and exposure to artificial lights have disturbed the circadian system because light is the major cue for synchrony.…”