320-16 - Regulatinggeneexpressioninbacteria theoperonmodel

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Regulating gene expression in bacteria - the operon model -   regulatory proteins  bind specific DNA sequences  to control  gene expression -   allosteric  proteins –> enable conditional gene expression -   polycistronic  (multiple genes) transcripts –> coordinated   regulation (bacteria only) -   multilevel  regulation transcription, translation, enzyme function Text chapter 17, question bank B
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Protein synthesis is expensive! • in energy (ATP, GTP) • in C, N => genes should be expressed only when needed. Cells must adapt to changing conditions nutrients stress time of day sensory experience - learning - require different sets of proteins
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gene regulation in bacteria • operons clusters of  functionally related  genes expressed in a  polycistronic  transcript and  coordinately regulated.   • the lac operon   encodes enzymes that convert  lactose  to  glucose • sigma proteins (but how is sigma protein expression regulated?) RNA polymerase
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Bacterial growth on sugar mixtures  (Monod , 1940-41) Log (cell number) time glucose “diauxie”  glucose +  lactose only glucose used lactose used “enzymatic adaptation?” 
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1941 Monod Observed diauxie 1943 Luria & Delbruck The fluctuation test: mutation in bacteria 1944 Avery, MacLeod & McCarty The transforming principle is DNA 1946-7 Lederberg & Tatum First cross & genetic map in E. coli K-12 1952 Hershey & Chase Only the DNA of phage enters the cell 1953 Hayes, Cavalli & Lederbergs F factor in E. coli mating 1953 Watson & Crick Structure of DNA 1954 Jacob & Wollman Zygotic induction of lysogenic phage 1955 Benzer Fine-structure mapping in phage; the cistron 1955 Wollman & Jacob Interrupted mating in bacteria 1958 Pardee, Jacob & Monod The PaJaMo experiment 1960 Jacob, Monod, et al The development of the operon concept 1961 Brenner, Jacob, & Meselson Experimental evidence for messenger RNA From diauxie to the operon
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Lactose catabolism in E. coli lactose permease glucose +   galactose galactosidase lacZ + lacY  + galactosidase permease
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lac  mutants  - cannot grow on lactose: - genes identified by complementation testing: lacZ  + lacY  x lacZ  lacY  + Diploid: grows on lactose? A: yes B: no lacZ + lacY lacZ lacY  + galactosidase permease Clicker question
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Inducibility Permease and galactosidase activities are high only in the presence  of lactose enzyme activity  time  lactose added   - the enzymes are  inducible  and  coordinately regulated;  lactose is an   inducer Adaptive enzymes? or inducible gene expression?
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Effects of lac mutations       if lactose  is:  absent       present lacI high high galactosidase wild type low high inducible constitutive low high lacY (none)  (none) lacZ inducible not made on the activity of…
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320-16 - Regulatinggeneexpressioninbacteria theoperonmodel

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