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Microbial Genetics (Micr340)

Lecture 16 delves into global regulatory mechanisms that control multiple operons in microbial genetics. Focused on how cells respond to major environmental changes, this session explores the impacts of nutrient and growth limitations as well as stress. Key concepts include catabolite repression, the role of cAMP and CAP (CRP) in sugar utilization, and the importance of nitrogen as an essential nutrient. We discuss the assimilation pathways for nitrogen and the regulation of Ntr operons in bacteria, including the two-component system involving glnA, ntrB, and ntrC operons in E. coli.

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Microbial Genetics (Micr340)

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  1. Microbial Genetics (Micr340) Lecture 16 Global Regulatory Mechanisms Note: a hand-out for Lecture 15 was uploaded into course web folder

  2. Global regulation • Global regulatory mechanisms: regulatory systems within cells that simultaneously regulate numerous operons in response to major changes in the environment • These systems respond to these factors: • Nutrient limitation • Growth limitation • Stress

  3. Catabolite-sensitive operons • Regulon: a large number of operons that are controlled by a single regulatory protein. • Catabolites: smaller molecules resulting from the metabolic breakdown (catabolism) of larger molecules. • Catabolite repression: a mechanism for ensuring that the cell will preferentially use the best carbon and energy source available.

  4. Preferential utilization

  5. cAMP and cAMP-Binding Protein • cAMP: cyclic AMP is similar to AMP, except the phosphate is attached to both 5’- and 3’ hydroxyl groups of the sugar. • In E. coli, there is a cAMP-dependent regulatory system that controls preferential utilization of sugar sources • CAP (catabolite gene activator protein), also known as CRP (cAMP receptor protein), is the global activator of catabolite sensitive operons

  6. Glucose inhibits cAMP synthesis and uptake of other sugars

  7. In absence of Glucose……. Lactose

  8. Regulation of lac by CAP-cAMP

  9. CAP-cAMP and other opeons • gal operon

  10. CAP-cAMP and other opeons • ara operon

  11. Nitrogen nutrient • Nitrogen is a component of many biological molecules thus is an essential nutrient source • Bacteria could use both inorganic (ammonia and nitrate) and organic nitrogen sources • Some bacteria can even use (fix) atmospheric nitrogen (N2), unique on earth.

  12. Pathways of nitrogen assimilation • Ammonia is the preferred source of nitrogen for most bacteria • Other forms of nitrogen must be reduced to ammonia before they can be used in a process called assimilatory reduction • The process of ammonia being integrated (assimilated) into an organic compound of biosynthetic pathways is called nitrogen assimilation

  13. Pathways of nitrogen assimilation

  14. Regulation of Ntr operons

  15. Two-component system

  16. Two-component system

  17. The glnA-ntrB-ntrC operon of E. coli

  18. Sigma factors define promoters

  19. Model of Activation ofp2 promoter

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