Molecular level biological clock

Sleep Disorders

Circadian rhythms have been found in living beings ranging from unicellular bacteria to higher mammals. Temporal orchestration of rhythmic protein activity and organelle function results in daily changes in the physiology of the organism. Most animals and plants have cycles tied to the sun. Some plants and animals in tidal regions have cycles that also correlate with the moon and tides.

Scientists have determined that the molecular timing mechanism (a.k.a. biological clock) works at the cellular level. Mammalian cells in a petri dish, separate from the rest of the animal, have a time cycle. Inside the cell, proteins are transcribed and translated in a feedback loop.

This cycle in turn regulates transcription of a large number of genes. At the organism level, a master circadian oscillator in the brain’s hypothalamic suprachiasmatic nucleus (SCN) orchestrates tissue specific rhythmic activities. The cycle is played out in aspects of both behavior and physiology.

The 2-process model of waking and sleeping proposes that the circadian cycle works in parallel with a homeostatic process of sleep desire build-up. More here.

In the early 20th Century scientists started seeing circadian patterns in animal behavior and showed that light-dark cycles affect the sleep patterns of mammals. In the 1930s the term “biological clock” was first used and in the 1960s it was shown that injuries to the hypothalamus area of the brain led to disruptions in the circadian cycle. Circadian cycles are still a major area of research for biologists and physiologists. We still don’t understand much about the brain and the circadian cycle’s relationship to sleep.

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