[Molecular mechanisms of circadian clock functioning].

Most physiological processes of all organisms are rhythmic with a period of about 24 h and are generated by an endogenous biological CLOCK present in all cells. However, there is also a central CLOCK--the primary circadian pacemaker which is localized in the suprachiasmatic nuclei of the mammalian hypothalamus. Factors of groups Period (PER1, PER2 and PER3), BMAL (BMAL1 and BMAL2), CRYptochromes (CRY1 and CRY2) as well as some other factors are the components of this circadian CLOCK system.