Lin Flashcards
Describe the function of the structural elements in a typical bacterial core promoter. What is the function of -35 and -10 elements in bacterial promoters?
They are the consensus sequence elements in the promoter that bind the σ subunit together with other subunits of bacterial RNA polymerase.
Describe the function of the structural elements in a typical bacterial core promoter. Which subunit of bacterial RNA polymerase increases the affinity and specificity for binding of the polymerase to the promoter?
σ subunit
What are the four steps of bacterial transcription initiation?
- The polymerase binds to the core promoter
- The polymerase unwinds the DNA near the transcription start site
- The polymerase initiates mRNA synthesis
- Promoter clearance in which the polymerase without σ subunit moves away from the promoter
What is generated by each of these steps (transcription initiation by bacterial RNA polymerase)?
- The polymerase binds to the core promoter: CLOSED BINARY COMPLEX
- The polymerase unwinds the DNA near the transcription start site: OPEN BINARY COMPLEX
- The polymerase initiates mRNA synthesis: TERNARY COMPLEX
- Promoter clearance in which the polymerase without σ subunit moves away from the promoter: ELONGATION COMPLEX
How do different σ factors induce different gene expression?
Different σ factors recognize and promote binding of RNA polymerase to different -35 and -10 elements that are in different core promoters controlling expression of different genes.
E. coli cells are growing in a medium containing lactose but no glucose. Indicate whether each of the following changes or conditions would increase, decrease, or not change the expression of the lac operon. Addition of a high concentration of glucose
cAMP concentration will be low, and, without bound cAMP, CRP will not bind to CRP site to facilitate RNA polymerase binding to lac promoter
E. coli cells are growing in a medium containing lactose but no glucose. Indicate whether each of the following changes or conditions would increase, decrease, or not change the expression of the lac operon. A mutation that prevents dissociation of the lac repressor from the operator
the mutant lac repressor will always bind to lac operator blocking RNA polymerase binding to lac promoter
E. coli cells are growing in a medium containing lactose but no glucose. Indicate whether each of the following changes or conditions would increase, decrease, or not change the expression of the lac operon. A mutation that completely inactivates β-galactosidase
siince β-galactosidase activity is required to produce allolactose (the inducer) from lactose, lac repressor will remain bound to the lac operator even in the presence of lactose, and the lac operon genes will not be induced
E. coli cells are growing in a medium containing lactose but no glucose. Indicate whether each of the following changes or conditions would increase, decrease, or not change the expression of the lac operon. A mutation that completely inactivates galactoside permease
in the absence of galactoside permease activity, no lactose can enter the cell to be converted to allolactose and induce the dissociation of lac repressor from lac operator
E. coli cells are growing in a medium containing lactose but no glucose. Indicate whether each of the following changes or conditions would increase, decrease, or not change the expression of the lac operon. A mutation that prevents binding of CRP to its binding site near the lac promoter
without binding of CRP to its binding site near the lac promoter, CRP cannot facilitate the binding of RNA polymerase to lac promoter
How would transcription of the E. coli trp operon be affected by the following manipulations of the leader region of the trp mRNA? Increasing the distance (number of bases) between the leader peptide gene and sequence 2
Less attenuation of transcription. The ribosome completing the translation of sequence 1 would no longer overlap and block sequence 2; sequence 2 would always be available to pair with sequence 3, preventing formation of the attenuator structure.
How would transcription of the E. coli trp operon be affected by the following manipulations of the leader region of the trp mRNA? Increasing the distance between sequences 2 and 3
More attenuation of transcription. Sequence 2 would pair less efficiently with sequence 3; the attenuator structure would be formed more often, even when sequence 2 was not blocked by a ribosome.
How would transcription of the E. coli trp operon be affected by the following manipulations of the leader region of the trp mRNA? Removing sequence 4
No attenuation of transcription. The only regulation would be that afforded by the trp repressor.
How would transcription of the E. coli trp operon be affected by the following manipulations of the leader region of the trp mRNA? Changing the two Trp codons in the leader peptide gene to His codons
Attenuation loses its sensitivity to Trp tRNA. It might become sensitive to His tRNA.
How would transcription of the E. coli trp operon be affected by the following manipulations of the leader region of the trp mRNA? Eliminating the ribosome-binding site for the gene that encodes the leader peptide
Attenuation would rarely, if ever, occur. Sequences 2 and 3 always block formation of the attenuator.
