320-16 - Regulating gene expression in bacteria the operon...

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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 - a carbon & energy source • 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 O b served diauxie 1943 Luria & Delbruck T he fluctuation test: mutation in bacteria 1944 Avery, MacLeod & McCarty T he transforming principle is DNA 1946-7 Lederberg & Tatum First cross & genetic map in E. coli K-12 1952 Hershey & Chase O n ly 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 Z ygotic induction of lysogenic phage 1955 Benze r F i ne-structure mapping in phage; the cistron 1955 Wollman & Jacob I n terrupted mating in bacteria 1958 Pardee, Jacob & Monod T he PaJaMo experiment 1960 Jacob, Monod, et al T he 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 - In lacI mutants, lacZ and lacY are expressed constitutively low high lacY (none) (none) lacZ inducible not made on the activity of…
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