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Regulatory Proteins: Regulation by Repression
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Why do different kinds of control mechanisms exist? Cells contain a diverse set of different mechanisms for controlling gene activation. In general, they type of mechanism controlling the synthesis of a gene product depends on the product’s function. If a product is involved in an catabolic pathway then gene expression will be stimulated by initial substrates of the pathway and repressed by final products of the pathway. Initial substrate molecules can either inactivate repressor proteins or induce activator proteins. Final product molecules would activate repressor proteins. Using these types of control mechanisms the genes for the pathway molecules could be turned on when there is a lot of the substrate molecules and turned off when there is a lot of the of the final product.

View the animation below, then complete the quiz to test your knowledge of the concept.





1A repressor protein...
A)binds to the DNA molecule and prevents transcription.
B)binds to the RNA polymerase preventing messenger RNA synthesis.
C)is unable to bind to the DNA molecule and prevent transcription.
D)is a structural protein.
E)is made in the absence of glucose.


2When a microorganism such as E. coli is grown on glucose...
A)it is unable to produce ATP.
B)it is capable of amino acid production.
C)it is incapable of amino acid production.
D)it is unable to produce its peptidoglycan layer.
E)it is unable to synthesize a cell wall.


3Which of the following is not true for activators?
A)Activators bind directly to the DNA.
B)Activators must react with the substrate that they regulate before binding with DNA.
C)The activator cannot bind to the DNA in the absence of an inducer.
D)Activators regulate some degradative pathways.
E)Activators facilitate transcription.


4Some degradative pathways are regulated by an activator protein. An activator is a regulatory protein that facilitates transcription by binding to DNA.
A)True
B)False


5Regulation of degradative pathways involving an activator that is activated by an inducer is referred to as positive control.
A)True
B)False





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