Prokaryotic Gene Regulation
Shown here is the lac operon. Lac I, Z, Y, and A are all genes that encode different enzymes. P is the promoter; O is the operon. The blue oval is RNA polymerase. When there is no lactose present, lac I blocks RNA polymerase and enzymes necessary for lactose metabolism are not created. When lactose is present, a small amount enters the cell and changes the shape of the molecule, unblocking RNA polymerase and allowing the creation of these enzymes.
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Transcription
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mRNA Degradation
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http://www.emunix.emich.edu/~rwinning/genetics/proreg.htm lac operon
http://www.nature.com/scitable/topicpage/gene-expression-14121669 Active/Inactive Repression
http://www.nature.com/scitable/topicpage/gene-expression-14121669 Active/Inactive Repression