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Name: Cathy
Status: Student
Grade:  N/A
Location: FL
Country: United States
Date: January 2005


Question:
What controls the RNA to be there to do it's magic? what would you guess is the controller that guides these actions....something has to regulate the regulator?



Replies:
The enzyme, RNA polymerase, synthesizes mRNA using one of the DNA strands as a template. In bacteria, whether or not a gene can be transcribed into mRNA is controlled by repressor proteins that sit on the operator region of the gene. The operator region is where RNA polymerase initiates transcription of the gene into mRNA. When the repressor protein is attached to the operator region, it blocks the RNA polymerase molecule from binding to the operator and no mRNA can be synthesized. The repressor protein can be knocked off the operator by the presence or absence of certain other molecules in the cell. For example, when the sugar lactose is present in E. coli, the repressor protein for the lactose operon, is inactivated and detaches from the operator gene at which point RNA polymerase can begin making the mRNA that codes for the synthesis of the enzyme lactase which catalyzes the digestion or splitting of lactose into glucose and galactose.

This is a negative control mechanism which helps the cell conserve energy. When there is no lactose around, the cell is not bothering to make lactase. It is called a negative control mechanism because when the control mechanism is functioning it shuts down the system, like the high temperature setting on a thermostat.

Ron Baker, Ph.D.



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