biol lec 6

Biol lec 6 - Prevents transcription in the absence of lactose In the absence of lactose Repressor protein is bound to Operator DNA sequence

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Prevents transcription in the absence of lactose In the absence of lactose · Repressor protein is bound to Operator DNA sequence · Repressor protein physically blocks RNA Polymerase · No transcription of lac Z, lac Y and lac A What happens in the presence of lactose? · Lactose is transported into cell and converted into allolactose · Allolactose binds to Repressor Protein · Now repressor cannot bind DNA · RNA polymerase is not blocked · Lac Z, lac Y, lac A are all transcribed · Polycistronic mRNA is translated -one message has coding sequence for multiple protein products -only in polymeras Repressor protein negatively controls expression of lac operon · Regulatory protein TURNS OFF transcription · Transcription on only when the repressor is not active (can’t bind DNA) Lac operon is also positively regulated by Catabolite Activator Protein (CAP) · Positively regulated 1) Regulatory protein TURNS ON operon 2) Active CAP binds at 5’ end of promoter to help RNA polymerase bind 3) CAP needs cAMP to be active · cAMP 1) only made when there’s low glucose in cell CAP allows cell to determine if glucose is present · glucose 1) simple sugar 2) easier to metabolize than lactose
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This note was uploaded on 01/18/2012 for the course BIO 101 taught by Professor Martin during the Fall '08 term at Rutgers.

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Biol lec 6 - Prevents transcription in the absence of lactose In the absence of lactose Repressor protein is bound to Operator DNA sequence

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