Lect12-KR

Lect12-KR - Regulatory mechanisms II PMB/MCB 112 Specific...

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Regulatory mechanisms II PMB/MCB 112 September 27, 2010
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Specific regulatory mechanisms -control activity of one of a few enzymes -control synthesis of one or a few proteins Feedback inhibition Transcriptional repressors + corepressors/inducers Transcriptional activators + coactivators In the examples shown, the purpose was to respond to one new condition (adding a specific sugar, running out of a single amino acid) But bacteria must often respond to complex environmental changes, or undergo sweeping changes in their physiology These responses are accomplished by global regulatory mechanisms
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Catabolite repression Bacteria usually live in environments with mixed carbon sources Catabolite repression allows the bacterium to use the most efficient carbon source first (often the one most easily fed into the glycolytic pathway) Diauxic growth curve of cells grown on a mixture of glucose and lactose: Lag in growth occurs when glucose is gone, and cells must make new enzymes to use lactose (or another carbon source)
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CAP catabolite activator protein cAMP RNAP σ factor -35 -10 tx Genes that are regulated by catabolite repression contain a binding site for CAP. When CAP binds cAMP, it can bind DNA and activate tx by RNAP. glucose cAMP In the absence of glucose, transcription of genes for alternative sugar utilization is activated by CAP CAP is an activator, and cAMP is its co-activator
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Many operons that have specific repressors or activators are ALSO regulated by catabolite repression Examples are the lac , mal , and ara operons Specific ( lac repressor) and global (CAP) regulatory mechanisms are used in combination cAMP-CAP only binds in the absence of glucose Lac repressor cannot bind in the presence of lactose
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Transcription of carbon utilization genes is linked to metabolism through the PTS system Glucose PRESENT Enz IIa inhibits uptake of alternative sugars by binding
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This note was uploaded on 01/19/2011 for the course C 112 taught by Professor Ryan during the Fall '10 term at Berkeley.

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Lect12-KR - Regulatory mechanisms II PMB/MCB 112 Specific...

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