The circadian clock is essential in many organisms. The circadian timing system enables the physiological and behavioral adaptation to the external geophysical changes through the regulation of the temporal cellular processes (Lehmann et al., 2015).
In mammals, the master pacemaker can be found in the suprachiasmatic nucleus (SCN). The master clock in the SCN regulates the peripheral clocks in the body cells in various organs, and control the timing of physiological and behavioral activities.
At the cellular level, every single cell is running with its own clock (Fuhr et al., 2015). With the synchronization of these individual clocks, the main pacemaker is also involved in the entrainment and communicate via its signals.
The clock genes and the oscillations of gene expressions are involved in the temporal regulation of various molecular and cellular activities. For example, the CLOCK/BMAL complex is associated with various positive and negative interactions in the networks of feedback-loops (Fuhr et al., 2015). Such feedback-loops are essential for the gene expression oscillations.
Chronobiology, especially circadian systems biology, provides interdisciplinary studies of the circadian systems at cellular and organismal levels.
Fuhr L, Abreu M, Pett P, Relógio A. Circadian systems biology: When time matters. Comput Struct Biotechnol J. 2015 Jul 17;13:417-26. doi: 10.1016/j.csbj.2015.07.001.
Lehmann R, Childs L, Thomas P, Abreu M, Fuhr L, Herzel H, Leser U, Relógio A. Assembly of a comprehensive regulatory network for the mammalian circadian clock: a bioinformatics approach. PLoS One. 2015 May 6;10(5):e0126283. doi: 10.1371/journal.pone.0126283.