Regulation of gene expression

1. Regulation of gene expression Premedical - Biology

2. Regulation of gene expression in prokaryotic cell - Operon units, system of negative feedback in eukaryotic cell come at any stage of gene expression and proteosynthesis. Important are noncoding RNAs.

4. Operon model is a functional unit common in bacteria and phages. Activation and inhibition of transcription are regulated in response of conditions in environment. Prokaryotic genetic information is not divided into introns and exons.

5. Operon • is coordinately regulated clusters of genes, which are transcribed into one mRNA (polygennic mRNA,polycystron transcript) • are genes for particular metabolic pathway and are regulatedby commonpromotor andareorderedon DNA following each other

6. Escherichia coli Lac operon, Trp operon– model systems = metabolic pathways of • utilization of lactosegen lacZ, lacY, lacA, catabolic pathway with negative and positive regulation • enzymes for TRP synthesis, anabolic pathway with negative regulation

7. each operon consists of • promoter (for RNA polymerase) • operator (for repressor) • several structural genes • terminator repressor = allosteric protein encoded by regulatory gene co-repressor = product molecule inducer = substrate molecule

8. Lac operon - negative regulation • regulatory gen produces repressor, which binds operator and causes thatRNAP is notableto initialize transcription • in the presence of lactoserepressor is released from operator. The repressor is changed by inducer / lactose RNA polymerasestarts the transcription. In 2-3 minutesthe amount of enzymes is increased 1000x

9. Lac operon - negative regulation

10. Lac operon - positive regulation In the presence of glucose, E. coli preferentially uses glucose for decomposing. If is low level of glucosis, the cAMP is increased. CAP „Catabolite activator protein“ in the presence of cAMP attaches promotor and activates the transcription. CAP is allosteric regulatory protein

11. Lac operon - positive regulation Summary: Lac operon is active only in time, when the activator CAP+cAMP is attached on promotor (no glucose) and when is not present represor on operator(lactose present)

12. Gene expression of eukaryotic cells • each cell maintains specific program / differential gene expression • one mRNA carries information for one gene(monogennic mRNA) • posttranscription modifications of RNA RNA processing and splicing • regulation system is performed at the several levels = transcription, translation, protein activation + secretion

13. Six steps at which eucaryotic gene expression can be controlled

14. more complicated regulative system • chromatin changes • transcription • processing RNA • transport to cytoplasm • degradation of mRNA • translation • cleavage, chemical modification • protein degradation

15. Stages in gene expression in eukaryotic cell

16. 1. Chromatin changes • Heterochromatin is highly condensed that is why transcriptional enzymes can not reach the DNA • Acetylation / deacetylation of histons • Methylation [cytosin] - inactive DNA is highly methylated DNA methylation and histone de-acetylation repress the transcription.

17. DNA methylation is esential for long-term inactivation of genes during cell differentiation Gene imprinting in mamals • methylation constantly turns off the maternal or the paternal allele of a gene in early development • certain genes are expressed in a parent-of-origin-specific manner Epigenetic inheritance

18. 2. Transcription Important proteins that bind DNA and facilitate or inhibit RNA polymerase to bind. They are a part of transcription initiation complex. Transcription factors: general transcription factors for all protein-coding genes specific transcription factors – transcription of particular genes at appropriate time and place • enhancers, activators, inhibitors, repressors

19. Eukaryotic gene and transcript

20. Cell-type specific transcription: Genes encoding the enzymes of one metabolic pathway are scattered over the different chromosomes - coordinated control in response of chemical signals from outside the cell. The cell accept signals by receptors. Signal transduction pathways activate transcription activators or repressors.

21. Signal transduction pathways

22. 3. Processing RNA Post-transcriptional modifications Alternative splicing The same primary transcript, but different the mRNA molecule from it (exons and introns) 4, 5. transport of mRNA / degradation Lifespan of mRNA is important for protein synthesis.

23. At the initiation stage – regulatory proteins bind the 5’ end of the mRNA with the cap. Activation or inactivation of protein factors to initiate translation 6. Translation

24. 7. Cleavage, chemical modifications Cleavage Post-translational modifications Regulatory proteins [products] are activated or inactivated by the reversible addition of phosphate groups / phosphorylation Sugars on surface of the cell / Glycosylation

25. Polypeptide chain may be cleaved into two or three pieces • Preproinsulin • Proinsulin - disulfide bridges • Insulin • Secretory protein

26. Post-translational modifications Acid/base - act/inact Hydrolysis – localization, act/inact Acetylation - act/inact Phosphorylation - act/inact Prenylation - localization Glycosylation - targeting

27. Various steps in the synthesis and assembly of collagen fibrils

28. 8. protein degradation Lifespan of protein is strictly regulated Protein for destruction is attached by a small protein ubiquitin. Protein complexes Proteasomes are places of degradation.

29. Thank you for your attention Campbell, Neil A., Reece, Jane B., Cain Michael L., Jackson, Robert B., Minorsky, Peter V., Biology, Benjamin-Cummings Publishing Company, 1996 –2010.