The circadian clock: a manager of biochemical processes within the organism

J Neuroendocrinol. 2003 Apr;15(4):339-43. doi: 10.1046/j.1365-2826.2003.00992.x.


The periodic succession of night and day has influenced life on earth for millions of years. Many organisms have "internalized" this periodic change in the form of the circadian clock. Its main function is to organize the time course of biochemical, physiological and behavioural processes thereby optimizing an organism's performance in anticipating changing environmental conditions. Therefore, it is important to understand the underlying mechanisms that connect the core pacemaker, which is located in the suprachiasmatic nuclei (SCN) of the hypothalamus, with peripheral organs. Several laboratories set out to identify genes that are under the influence of the circadian clock. It appears that the circadian clock coordinates transcription of key metabolic pathways thereby orchestrating the time course of physiological and behavioural processes. We review these investigations and put our experiments, the comparison of gene expression in SCN tissue of Per2 mutant and wild-type mice, in the context of these findings.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Animals
  • Biological Clocks / genetics*
  • CLOCK Proteins
  • Cell Cycle Proteins
  • Cells, Cultured / physiology
  • Circadian Rhythm / genetics*
  • Fibroblasts / physiology
  • Gene Expression Regulation / genetics*
  • Gene Expression Regulation / physiology
  • Liver / physiology
  • Mammals
  • Mice
  • Mice, Mutant Strains / genetics
  • Myocardium / metabolism
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism
  • Period Circadian Proteins
  • Rats
  • Suprachiasmatic Nucleus / physiology
  • Tissue Distribution / genetics
  • Trans-Activators / genetics
  • Trans-Activators / metabolism
  • Transcription Factors


  • Cell Cycle Proteins
  • Nuclear Proteins
  • Per2 protein, mouse
  • Per2 protein, rat
  • Period Circadian Proteins
  • Trans-Activators
  • Transcription Factors
  • CLOCK Proteins
  • Clock protein, mouse
  • Clock protein, rat