B 1105 Homework #2 (based on 2 and 3) Instructor: Cabrera 11. A strain of bacter
ID: 150625 • Letter: B
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B 1105 Homework #2 (based on 2 and 3) Instructor: Cabrera 11. A strain of bacteria factor. The temperatures. possesses a temperature-sensitive mutation in the gene that encodes the sigma mutant bacteria produce a sigma factor that is unable to bind to RNA polymerase at elevated What effect will this mutation have on the process of transcription when the bacteria are grown at elevated temperatures? (Consider BOTH the initiotion of new transcriptions and transcriptions that have already been storted before the temperature was elevoted) 14 pts 12a. In transcription, what is the difference between positive and negative regulation? (3 pts) 12b. golB is a gene in E. coli which encodes an enzyme that is required for cells to use the sugar galactose. Suppose that a repressor regulates the expression of the golB gene by binding to the DNA near the promoter of gals and therefore prevents its transcription. Would you expect the repressor to bind DNA in the presence or absence or galactose? Explain your answer. [3 pts 12c. You identified a E. coll mutant that transcribes galB in BOTH the presence and absence of galactose. Which part of the golB transcriptional regulation may be affected in the mutant? Explain your answer briefly.[3 pts]Explanation / Answer
11.The binding of the sigma factor to the RNA polymerase core enzyme forms the RNA polymerase holoenzyme. Only the holoenzyme binds to the promoter. without the sigma factor, RNA polymerase will be unable to bind the promoter and transcription initiation will not take place. Any RNA polymerase that has completed transcription initiation and has begun elongation will complete transcription because the sigma factor is not needed for elongation. however, no further initiation will be possible at the elevated temperatures.
12.negative regulation.An aporepressor binds to a co repressor to form the active repressor. The active repressor can then bind to the DNA and prevent transcription from occurring.
positive regulation of transcription:-
The default state of transcription is turned "off" unless an activator turns it "on"
- turns on the expression of a gene
- can be inducible or repressible.
12..c. DNA binding domain, and the transcription activation domain.
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