Cell Signaling

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Every cell in the human body contains the whole genome. So why do brain cells look different from skin cells? Although every cell has the genetic information to produce each protein only some genes are expressed. So the gene expression has to be regulated somehow. It turns out, that not only variation of gene expression throught space (spatial variation) occurs, but also throughout time (temporal variation).

Gene regulation occurs on different levels:

  • DNA level
    • recombination of DNA (DNA is cut and recombined alternatively)
    • inversion of DNA (DNA is cut and inverted)
  • Transcriptional level
    • transcription initiation regulation through transcription factors
    • transcriptional regulation through global regulators called sigma factors
    • binding of DNA to histone proteins prevents DNA transcription
    • alternative splicing
    • RNA stability: RNA can be actively degraded by proteins
  • Translational level
    • binding of RNA to metabolites
    • micro RNAs (small RNAs ~20bp) that bind mRNA, thereby prohibiting translation
    • 5'capping controlles RNA stability and translocation out of the nucleus
  • Posttranslational level
    • Protein degradation
    • Protein phosphorylation activates otherwise inactive proteins

One of the best understood control mechanism is the regulation of transcription initiation through transcription factors. The first example of transcriptional regulation that was worked out, is the lactose utilisation system of the bacteria E. coli known as ''lac'' operon.