Question

Page < 2 > of 2 D. The trp operon would be expressed at high levels, comparable to its expression in the absence of trp 6. Based upon what you have learned about the E. coli trp operon, what could you say about expression of its structural genes in cells with large amounts of environmental trp, but expressing a mutant trp repressor that is unable to bind trp? A. The trp operon would be completely repressed due to the abundance of trp B. The trp operon would be transcribed much less than it would be if trp were absent, but would not be completely repressed C. The trp operon would be induced by the abundance of trp D. The trp operon would be expressed at high levels, comparable to its expression in the absence of trp 7. Based upon what you have learned about the E.coli trp operon, how would you have to modify the trp regulatory factors and elements to eliminate all repression in the presence of trp-causing the same amount of tror operon expression as when trp is absent? Select all of the modifications listed here that would be necessary A. Delete the leader sequence after the Shine-Dalgarno sequence B. Express a regulatory protein that always binds the operator, regardless of whether it binds trp C Mutate the operator sequence so that it cannot bind the trp regulatory protein D. Eliminate the promoter region E Move the uracil-rich sequence from immediately after region 4 to immediately after region 3 8. You have identified an unusual molecule, "OSU," that is only synthesized in bacteria living in the roots of the buckeye tree. Osu regulates expression of the OSU operon, thereby regulating transcription of the enzymes responsible for its synthesis. When OSU levels are high, OSU binds to a regulatory protein, removing it from the OSU promoter and inhibiting transcription of these structural genes. What type of regulation is present here? A Negative inducible 8. Negative repressible C. Positive inducible D. Positive repressible 9. Mannitol regulates expression from an operon that contains structural genes needed for mannitol catabolism. When mannitol and glucose are both present, the operon is repressed, but when mannitol is present and glucose is absent, the operon is expressed What would most likely happen when bacteria were exposed to mannitol but no lucose along with an inhibitor of adenylyl cyclase A Expression of this operon 3. Repression of this operon

Answer 1

6. The trp operon encodes structural tryptophan genes that are needed for Trp biosynthesis. trpR codes for the repressor protein that binds to environmental trp to block the transcription of the operon. Both repressor and Trp bound together form the holo repressor complex. In the question, large amount of environmental trp but a mutant trp repressor is present. So repressor is unable to bind to the operon and prevent transcription. However high Trp will attenuate the operon and will terminate the transcription at the attenuator site. So only a basal level of the Trp operon will be transcribed. So the correct option is: Option B.