1 / 35

The lac operon – An inducible operon

The lac operon – An inducible operon. Genes are either cis (coupling) acting Genes affect those adjacent to themselves Operator and structural genes Or trans (repulsion) acting Genes affect other genes that are not adjacent to themselves Implies the action of a diffusible product

akiva
Download Presentation

The lac operon – An inducible operon

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The lac operon – An inducible operon • Genes are either cis (coupling) acting • Genes affect those adjacent to themselves • Operator and structural genes Or • trans (repulsion) acting • Genes affect other genes that are not adjacent to themselves • Implies the action of a diffusible product • Regulator genes

  2. Trans (repulsion) acting genes • Genes that affect other genes • Are not adjacent to the genes they control • Regulator genes Implies the action of a diffusible product

  3. Genes that are cis (coupling) acting • Genes affect genes adjacent to themselves • Operator and structural genes

  4. The lac operon – An inducible operon • Bacteria are monoploid – one copy of each gene • Can make bacteria partially diploid (two copies of a gene) • Place another copy of the gene(s) on a plasmid (F’) • E.coli lac I mutant with a plasmid carrying a functional repressor gene will be designated: I - O + Z +/F’ I +

  5. The lac operon – An inducible operon

  6. The lac operon – An inducible operon

  7. The lac operon – An inducible operon

  8. The lac operon – An inducible operon

  9. The lac operon – An inducible operon

  10. plasmid E. Coli genome

  11. The lac operon – An inducible operon

  12. The lac operon – An inducible operon

  13. The lac operon – An inducible operon

  14. The lac operon – An inducible operon In F’ plasmid, an entire lac operon can be supplied. For example, I + O + Z - Y +/F’ I - O + Z + Y - What are the beta-galactosidase and permease activities with and without lactose in the E. coli strain with the above genotype?

  15. The lac operon • If E. coli cells are provided with both glucose and lactose, it preferentially metabolizes glucose rather than lactose. How do E. coli cells accomplish this? • Positive control and catabolite repression

  16. Positive Control and Catabolite Repression New Players: Cyclic AMP (cAMP) CAP (catabolite activator protein)

  17. Positive Control and Catabolite Repression High glucose low cAMP Low glucose high cAMP

  18. Positive Control and Catabolite Repression High glucose low cAMP Low glucose high cAMP

  19. Positive Control and Catabolite Repression High glucose low cAMP Low glucose high cAMP

  20. The cAMP-CAP complex interacts with the promoter (neither can bind the promoter of lac operon by themselves) CAP = Catabolite Activator Protein

  21. Facilitates the attachment of the RNA polymerase to the promoter – acts as an activator Must be a cAMP-CAP complex to bind to the promoter

  22. Positive Control and Catabolite Repression What would happen to the lac operon when: • Glucose present (+), but lactose absent (-)

  23. The cAMP-CAP complex is not formed (low cAMP), so CAP does not bind to the promoter (low) No transcription In addition, there is no inducer (lactose), so the active repressor is bound to the operator, and therefore the RNA polymerase cannot bind and transcribe the Lac operon genes

  24. Positive Control and Catabolite Repression What would happen to the lac operon when: • Glucose present (+), but lactose absent (-) • No transcription

  25. Positive Control and Catabolite Repression What would happen to the lac operon when: • Glucose present (+), but lactose absent (-) • No transcription • Glucose and lactose both present (+)

  26. The cAMP-CAP complex does not form (low cAMP) • The inducer (lactose) is present and inactivates the repressor • There is some transcription, but it is inefficient (no cAMP-CAP complex)

  27. Positive Control and Catabolite Repression What would happen to the lac operon when: • Glucose present (+), but lactose absent (-) • No transcription • Glucose and lactose both present (+) • Very little transcription

  28. Positive Control and Catabolite Repression What would happen to the lac operon when: • Glucose present (+), but lactose absent (-) • No transcription • Glucose and lactose both present (+) • Very little transcription • Glucose absent (-), but lactose present (+)

  29. The cAMP-CAP complex does form (high cAMP), facilitating the attachment of the RNA polymerase to the promoter The RNA polymerase is effectively attached to the promoter, enhancing transcription

  30. Positive Control and Catabolite Repression What would happen to the lac operon when: • Glucose present (+), but lactose absent (-) • No transcription • Glucose and lactose both present (+) • Very little transcription • Glucose absent (-), but lactose present (+) • A lot of transcription

  31. Positive Control and Catabolite Repression What would happen to the lac operon when: • Glucose present (+), but lactose absent (-) • No transcription • Glucose and lactose both present (+) • Very little transcription • Glucose absent (-), but lactose present (+) • A lot of transcription • Glucose and lactose both absent (-)

  32. cAMP pairs with CAP and can attach to the promoter No inducer (no lactose)No transcription Repressor stays bound to the operator

  33. Positive Control and Catabolite Repression What would happen to the lac operon when: • Glucose present (+), but lactose absent (-) • No transcription • Glucose and lactose both present (+) • Very little transcription • Glucose absent (-), but lactose present (+) • A lot of transcription • Glucose and lactose both absent (-) • No transcription

  34. Lac operon overview - animation http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter12/animation_quiz_4.html

More Related