Microbial Genetics (Micr340) Lecture 16 Global Regulatory Mechanisms Note: a hand-out for Lecture 15...
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Transcript of Microbial Genetics (Micr340) Lecture 16 Global Regulatory Mechanisms Note: a hand-out for Lecture 15...
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Microbial Genetics (Micr340)
Lecture 16Global Regulatory Mechanisms
Note: a hand-out for Lecture 15 was uploaded into course web folder
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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
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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.
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Preferential utilization
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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
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Glucose inhibits cAMP synthesis and uptake of other sugars
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In absence of Glucose…….
Lactose
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Regulation of lac by CAP-cAMP
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CAP-cAMP and other opeons
gal operon
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CAP-cAMP and other opeons
ara operon
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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.
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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
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Pathways of nitrogen assimilation
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Regulation of Ntr operons
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Two-component system
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Two-component system
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The glnA-ntrB-ntrC operon of E. coli
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Sigma factors define promoters
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Model of Activation ofp2 promoter