Chronobiology · Cell clocks · Circadian rhythms
All living beings are subject to biological rhythms, i.e. biological phenomena that repeat themselves at regular intervals such as a day, month or year. Animals, plants and unicellular organisms therefore possess an internal circadian rhythm that periodically controls processes in the body and behaviour, for example the sleep-wake rhythm.
Like a watch, however, the internal clocks of the organisms must also be set regularly. In the course of evolution, these inner clocks have developed which provide the body with decisive time information even in the absence of external influences such as light. This allows important metabolic functions, for example, to be optimally adapted to the changing conditions during the course of the day.
The circadian clock is divided into a central and many peripheral clocks. The central clock is synchronized by light and communicates with other peripheral or subordinate cell clocks, the clock genes (scientifically "Bmal-1") that are present in most cells of the body. The circadian rhythm, which clocks many different organic processes, follows a cycle of about 24 hours in humans.
Metabolism as clock generator of cell clocks · Clock genes
The peripheral cell clocks control the periodic metabolic processes in the respective organ by rhythmically activating certain genes. Even if these normally run synchronously with the central clock, according to newer findings they can be adjusted by external influences and decoupled from the central clock.
Many biochemical and physiological processes are subject to circadian rhythms. For example, body temperature, blood pressure and the hormone and immune systems are circadianly regulated.
In mammals, the circadian clock is divided hierarchically into a central clock located in the SCN of the hypothalamus which is known as the pacemaker, and peripheral clocks. The central clock adapts the 24-hour cycle to the external environmental timers and transmits the information to the peripheral clocks in the body tissue, which are coordinated by the central clock (Golombek & Rosenstein 2010).
At the molecular level, the intracellular clockwork is formed from mutually influencing positive and negative transcriptional-translational feedback loops (TTFL). The circadian oscillators are driven by the feedback loops of transcription and translation, whose oscillation frequency is about 24 hours even without an external timer. Decisive for the generation and maintenance of the 24h period is a precise interaction of the daily-periodic synthesis, modification and degradation of central clock proteins within their specific protein-protein and protein-nucleic acid interactions.