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Lecture 22 W11 - Lecture 22 Notes I Regulation of gene...

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Lecture 22 (3-09-11) Notes I. Regulation of gene expression can occur at multiple levels A. Transcriptional regulation – controlling the amount of mRNA that is made B. Translational regulation – controlling the amount of protein made from a mRNA C. Post-translational regulation – controlling the activity of a protein after it is synthesized D. In prokaryotes, because there is no partitioning of the sites of transcription and translation, all three levels of regulation can occur in quick succession II. Catabolism in E. coli (a bacteria found in our intestines) A. E. coli prefer to use glucose for energy because it is less expensive B. In the absence of glucose, other carbohydrates with high energy bonds can be used 1. lactose, a disaccharide C. An enzyme call beta-galactosidase (lacZ) can convert lactose into glucose + galactose 1. A molecule of ATP is required to convert galactose into glucose 2. Glycolysis yields two molecules of ATP for every glucose. Therefore, E. coli get a net anaerobic gain of three ATP from lactose, one less than when the carbohydrate is in the form of glucose (2 glucose yield 4 ATP) D. E. coli (and other bacteria) will always do what is most efficient (it’s a competitive world in the intestine). 1. When grown in the presence of lactose (and no glucose), E. coli expresses high levels of beta-galactosidase. Thus lactose is an inducer of beta-galactosidase.
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