Biology 311C Lecture 34 - November 14, 2011 Biology 311C...

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November 14, 2011 Biology 311C Lecture 34 Some genes are organized in units called operons (one shared promoter, several protein- coding genes, one long mRNA). Lac operons genes are usually turned off, but turned on in the presence of lactose sugar. When lactose is present, it is an inducer, the lac operons are turned on, the repressor in active, and the operon is on. Even though you have a long mRNA molecule, it can code for several proteins. The active repressor is made by a regulatory gene when it is transcribed to make mRNA. If there was a frame-shift mutation in the regulatory gene, beta galactosidase would constantly be produced. The active repressor is not produced so it can’t stop the operator and RNA polymerase can continuously transcribe. If a substitution mutation in the lac operon promoter (and RNA polymerase could not bind), none of the proteins from the genes will be made. They all have the same promoter so if there is no RNA polymerase, transcription will
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