1 / 11

Chapter 15.4

Chapter 15.4. Prokaryotic Gene Control. AP Biology Fall 2010. Lac Operon. http://www.youtube.com/watch?v=49siJ7XowhU&NR=1 Watch and take notes!. Negative Control of the Lactose Operon.

anitra
Télécharger la présentation

Chapter 15.4

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. Chapter 15.4 Prokaryotic Gene Control AP Biology Fall 2010

  2. Lac Operon • http://www.youtube.com/watch?v=49siJ7XowhU&NR=1 • Watch and take notes!

  3. Negative Control of the Lactose Operon • E. coli bacteria (common in the human digestive tract) can metabolize lactose because of a series of three genes that code for lactose-digesting enzymes

  4. Negative Control of the Lactose Operon • The three genes are preceded by a promoter and an operator • Altogether called an operon • http://www.youtube.com/watch?v=iPQZXMKZEfw

  5. Negative Control of the Lactose Operon • A regulator gene nearby codes for a repressor protein • Which binds to the operator when lactose concentrations are low and effectively blocks RNA polymerase’s access to the promoter  Not able to bind when repressor is bound

  6. Negative Control of the Lactose Operon • When milk is consumed the lactose binds to the repressor • Changing its shape and effectively removing its blockage of the promotor • Thus, RNA polymerase can now initiate transcription of the genes

  7. Positive Control of the Lactose Operon • The lactose operon is also subject to positive control by an activator protein called CAP • CAP: catabolite activator protein • cAMP: cyclic adenosine monophosphate • RNA polymerase will bind to the promoter if CAP is already there • In turn, CAP must first be activated by cAMP

  8. Positive Control of the Lactose Operon • When glucose is scarce, the CAP – cAMP complex forms and turns on the lactose metabolism genes • Converts lactose to glucose • Makes a promoter far more inviting to RNA polymerase • Complex called transcription factor • Why is this used? • E.coli cells pay far more attention to glucose than lactose • Lactose operon is not used much, unless there is no glucose

  9. Positive Control of the Lactose Operon • Glucose plentiful  ATP forms by glycolysis • Synthesis of enzyme necessary to synthesize cAMP is blocked • Glucose scarce  blocking ends, lactose available • CAP-cAMP complex forms • Lactose operon genes transcribed • Gene products allow lactose to be converted to glucose

  10. Positive Control of the Lactose Operon • Humans may develop lactose intolerance as we age due to declining concentrations of the lactose – digesting enzyme (lactase) • Too much lactose results and bacterial populations in the gut explode • Produces gas and diarrhea as by-products of their metabolism

More Related