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Signal transduction

Signal transduction

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Signal transduction

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  1. Signal transduction Джим Камашев

  2. Signal transduction and cell division

  3. Signal transduction in prokaryotes

  4. Regulation of Enzyme Activity Feedback Inhibition

  5. An allosteric enzyme has two binding sites, the active site, where the substrate binds, and the allosteric site, where the inhibitor (called an effector) binds reversibly

  6. glucose

  7. glucose

  8. These sugars must be proceeded before entering in glycolysis glucose arabinose lactose galactose maltose

  9. Induction of lac operon (negative regulation) (beta galactosidase)

  10. Expression of arginine biosynthetic pathway (Operon) (Arginine)

  11. trp arg aporrepresor + correpresor

  12. Maltose operon regulation (positive) (Absence of inducer - maltose) (maltose)

  13. Constitutive mutant (Oc)

  14. Constitutive mutant (I-)

  15. mutant non inducible (Is e Iq)

  16. Lac operator

  17. IPTG

  18. An Overview of Gene Regulation

  19. Negative Control of Transcription: Repression and Induction

  20. This transcriptional regulation involves allosteric regulatory proteins that bind to DNA. For negative control of transcription, the regulatory molecule is called a repressor protein and it functions by inhibiting mRNA synthesis.

  21. Positive Control of Transcription Positive control of transcription is implemented by regulators called activator proteins. They bind to activator-binding sites on the DNA and stimulate transcription. As in repressors, activator protein activity is modified by effectors.

  22. For positive control of enzyme induction, the effector promotes the binding of the activator protein and thus stimulates transcription

  23. Operon • bacterial operons – allows the bacteria to regulate its transcription/translation machinery using the environment • operons participate in metabolic control • turned on or off based on the metabolic requirements of the bacteria • operon: a functioning unit of genomic DNA containing a cluster of genes under the control of a single regulatory signal or promoter. The genes are transcribed together into an mRNA strand and. The result of this is that the genes contained in the operon are either expressed together or not at all.Several genes must be both co-transcribed and co-regulated to define an operon • e.g. trp-operon, lac-operon • promoter – controls transcription of multiple downstream genes that code for enzymes that synthesize a specific metabolic component (e.g. amino acid) • these downstream genes are called a transcription unit • also contains an operator region – on/off switch that ultimately controls the promoter and the downstream genes

  24. resumen

  25. In eukaryotes nuclear receptors are always bound to “operator” = response element • No inducer  recruits repressors • With inducer  recruits activators

  26. What does bacterium have to do ?

  27. diauxie

  28. Global Regulatory Mechanisms

  29. Global control systems regulate the expression of many genes simultaneously. Catabolite repression is a global control system, and it helps cells make the most efficient use of carbon sources.

  30. The phenomenon of catabolite repression has been observed in operons other than the lac operon. In fact, the expression of many operons that play roles in sugar metabolism and amino acid metabolism is affected by the presence of glucose. Examples are: the arabinose (ara) operon; the maltose (mal) operon; and, the histidine utilization (hut) operon. This is a GLOBAL CONTROL MECHANISM. • The global nature of the catabolite repression phenomenon makes sense. As long as glucose is present, it will be the preferred substrate for growth, so there will be no need for any of the other substances to be used and, consequently, for their operons to be expressed. • Catabolite repression is mediated through the effects that glucose transport into the cell has on the internal concentration of cyclic AMP (cAMP). The following "cartoon" shows how this works: • If glucose is abundant in the growth medium it will be transported in to the cell by the action the glucose transport system. As it is being transported, glucose is phosphorylated with the phosphate group being donated by a component of the transport system.The same component also activates the enzyme, adenylate cyclase. As long as the component is participating in glucose transport, it is not able to activate adenylate cyclase.The result is that as glucose is transported into the cell, the concentration of cAMP falls (because adenylate cyclase is not being activated to synthesize any more). • If there is little or no glucose in the growth medium, the glucose transport system is not operational. The phosphate donor component is now free to activate aadenylate cyclase.The result is that in the absence of glucose, the concentration of cAMP rises. • Thus there is an inverse relationship between [glucose] and [cAMP]. As one rises, the other falls.

  31. cAMP and CAP(catabolite activator protein)

  32. High glucose  low cAMP  no CAP binding to DNA  no activation Low glucose  high cAMP  cAMP-CAP binding to DNA  activation

  33. + glucosa - lactosa -> NO síntesis + glucosa + lactosa -> poca sínt. - glucosa + lactosa -> SI síntesis

  34. The lacoperon is under the control of catabolite repression as well as its own specific negative regulatory system

  35. The Stringent Response • is a global control mechanism triggered by amino acid starvation. ?

  36. ThealarmonesppGpp and pppGpp are produced by RelA, a protein that monitors ribosome activity.

  37. ppGpp Пи-пи-ДЖИ-пи-пи

  38. Other Global Control Networks Cells can control several regulons by employing alternative sigma factors. Alternative signal factors in Escherichia coli are shown in Table 8.2.

  39. Sigma factor binds DNA RNAP holoenzyme binds Sigma factor – DNA complex

  40. These recognize only certain promoters and thus allow transcription of a select category of genes. Other global signals include cold and heat shock proteins that function to help the cell overcome temperature stress.

  41. Table 8.1 shows examples of global control systems known in Escherichia coli.

  42. Sigma38 changes pol to respond to this regulation without repressors or activators Normal Transcription Osm promoters contain poised polymerases Osmotic shock Neutral osmolytes restore sigma70 function potassium glutamate accumulation, inhibited s70 transcription Poised polymerases begin transcription s38 polymerase produces neutral osmolytes key unresolved question: How does the weak acid salt induce the poised RNAP to escape?