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Understanding the Lac Operon: Mechanisms of Lactose Regulation in Bacteria

The lac operon is a key regulatory system in bacteria that controls lactose metabolism. It consists of genes coding for β-galactosidase, lactose permease, and transacetylase, regulated by the presence of lactose and glucose. When lactose is available, it binds to the repressor, allowing RNA polymerase to activate transcription of the operon. In contrast, high glucose levels lead to low cAMP and inhibited activation of the operon through the CAP complex. This intricate balancing act dictates how bacteria utilize lactose efficiently while managing energy resources.

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Understanding the Lac Operon: Mechanisms of Lactose Regulation in Bacteria

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  1. lacZ lacY lacA lacZ lacY lacA lacZ lacY lacA lacZ lacY lacA lacZ lacY lacA A A A A O O O O A O i i i i i Repressor lactose lactose/repressor RNA pol CRP cAMP CRP/cAMP complex CAP complex NO transcription Transcription occurs NO transcription Lac operon operator Regulatory gene activator P B-galactosidase lactose permease transcetylase

  2. Glucose glycolysis PEP ATP glucose Pyruvate IIA HPr EI IIC Kreb’s IIB glucose Low cAMP lactose Repressor lactose lactose/repressor RNA pol CRP cAMP CRP/cAMP complex CAP complex Lots of glucose Not taken up

  3. Glucose PEP Pyruvate IIA HPr EI Kreb’s This process slows down glycolysis ATP Not more glucose IIC IIB Adenylate cyclase Levels of cAMP increase lactose Repressor lactose lactose/repressor RNA pol CRP cAMP CRP/cAMP complex CAP complex

  4. Glucose PEP Pyruvate IIA HPr EI Kreb’s This process slows down glycolysis ATP Not more glucose IIC IIB Adenylate cyclase lacOp becomes active lactose Repressor lactose lactose/repressor RNA pol CRP cAMP CRP/cAMP complex CAP complex

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