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Lecture

Bio 13 Lecture 30 Notes.docx

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Department
Biology
Course
BIO-0013
Professor
Derek Mc Lachlin
Semester
Fall

Description
Lecture 30  Mutants Found – gene lacI­ • Always had B­galactosidase activity, no matter whether there was lactose or not • In normal cells, there must be some sort of off switch to conserve energy • Glucose and LacI protein are examples of negative control • Lactose is an example of positive control Repressor Protein regulates transcription of the lac operon genes • It’s a regulatory protein – always somewhat present in the cell • Lac operon has many different sites upstream from it • In absence of lactose, repressor is present – causes no transcription o Lac Operon genes OFF if no lactose present  Negative control is needed • Repressor binds to Operator sequence upstream from Lac Operon o Blocks RNA polymerase from transcribing Mutant Repressor Protein • No repressor present • The protein is not functional therefore RNA polymerase binds to the promoter for  the Lac Operon • Transcription begins Repressor protein with Lactose Present • Lactose serves as an inducer o It binds to the repressor protein o This complex cannot bind to DNA so transcription goes on • Lactose allosterically binds to the repressor and changes the shape How does E. coli choose glucose over lactose when both are available • Presence of glucose suppresses the production of the enzyme that breaks down  lactose • So there is no way that lactose can be used, must use glucose • cAMP is synthesized when glucose levels are low o ATP is converted to cyclic AMP and two phosphates via Adenylyl cyclase • Glucose inhibits the activity of Adenylyl cyclase – wont be able to make cAMP o Low A.C. and low cAMP so low transcription of the
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