module 7 lec 10 Flashcards
What type of operon is the Trp operon?
It is a repressible operon.
What is the role of the Trp operon?
The Trp operon regulates the synthesis of the amino acid tryptophan in bacteria.
How is the Trp operon typically regulated?
The Trp operon is repressed when tryptophan is abundant. The repressor binds to the operator to stop transcription.
What happens when tryptophan levels are low in the cell
The Trp operon is active, and genes for tryptophan synthesis are transcribed.
What molecule activates the repressor in the Trp operon?
Tryptophan acts as a corepressor by binding to the repressor, activating it to bind to the operator.
What does TrpR refer to in the Trp operon?
TrpR is the repressor gene that regulates the Trp operon.
How does TrpR+ affect Trp operon repression when tryptophan is present?
TrpR+ allows repression of the Trp operon in the presence of tryptophan (repressor binds to operator, stopping transcription).
What happens in the absence of tryptophan with TrpR+?
TrpR+ results in no repression, allowing transcription of the operon and production of tryptophan.
What is the role of TrpR- in the Trp operon?
TrpR- is a nonfunctional repressor that cannot bind to the operator, resulting in constitutive expression of the operon regardless of tryptophan levels
What happens when TrpR- is present and tryptophan is available?
Even with tryptophan, TrpR- cannot repress the operon, leading to high levels of tryptophan synthesis.
What is the difference in repression between TrpR+ and TrpR-?
TrpR+ represses the operon in the presence of tryptophan (low transcription), while TrpR- results in constant transcription regardless of tryptophan (high transcription).
What is attenuation in the context of the Trp operon?
Attenuation is a mechanism where the availability of charged tRNA (with tryptophan) controls the production of full-length mRNA.
How does tRNA charged with tryptophan affect Trp operon transcription?
: When tRNA is charged with tryptophan, it allows attenuation to occur, causing premature termination of transcription and thus preventing full-length mRNA production.
What happens if there is low tryptophan or low charged tRNA?
If tryptophan is low, attenuation does not occur, allowing full-length mRNA to be synthesized and the operon to be transcribed.
What role does tRNA play in Trp operon attenuation?
tRNA charged with tryptophan affects the formation of a hairpin loop in the mRNA, which regulates whether transcription continues or terminates prematurely.
What is the connection between attenuation and the Trp operon?
Attenuation in the Trp operon is a regulatory mechanism that controls gene expression based on the availability of charged tRNA and tryptophan levels.
How does the Trp operon use attenuation to regulate gene expression?
The Trp operon uses attenuation to prevent unnecessary synthesis of tryptophan by halting transcription when tryptophan is abundant (via charged tRNA).
What are regulons?
Regulons are groups of operons regulated by the same regulatory proteins, often in response to environmental changes or stress.
What is an example of a regulon in E. coli?
An example of a regulon in E. coli is the heat shock response, where several genes are activated to deal with heat-induced stress
How does E. coli respond to high temperature through a regulon?
At high temperatures, E. coli induces proteins that degrade damaged proteins and help refold proteins using molecular chaperones.
What mediates the heat shock response in E. coli?
The heat shock response in E. coli is mediated by special sigma factors that control the expression of stress response genes.
What is the role of sigma factors in regulons?
Sigma factors direct RNA polymerase to specific promoters, enabling the expression of genes involved in stress responses, like the heat shock regulon.
How are operons and regulons related?
Regulons consist of multiple operons that are regulated together by the same regulatory proteins, typically in response to a specific environmental signal.
sigma 32 and 70 do what
recognize promoter sequence for heat shock response
at high twmpweatures sigma 24 recognizes different promoter sequences on _____ gene and _____ is transcribed
rPOH; sigma 32
What are small RNAs (sRNAs)?
Small RNAs (sRNAs) are short RNA molecules that regulate gene expression by interacting with mRNA to inhibit or activate translation.
How do sRNAs usually inhibit translation?
sRNAs typically inhibit translation by base-pairing with the ribosome binding site (RBS) of the mRNA, preventing ribosome attachment
Can sRNAs activate translation?
Yes, sRNAs can activate translation by disrupting stem-loop structures in the mRNA, making the ribosome binding site accessible.
What other effect can sRNAs have on mRNA?
Some sRNAs lead to mRNA degradation, either by promoting degradation directly or by affecting the stability of the mRNA.
How do sRNAs typically work?
sRNAs usually work by base-pairing with complementary regions of the mRNA, either blocking translation or promoting mRNA degradation.
What is one mechanism by which sRNAs can activate gene expression
sRNAs can activate gene expression by disrupting secondary structures (like stem-loops) in mRNA, freeing up the ribosome binding site for translation.
Are sRNAs involved in mRNA degradation?
Yes, some sRNAs can lead to mRNA degradation, often by recruiting ribonucleases to cleave the mRNA.
Are sRNAs involved in prokaryotic gene regulation?
Yes, sRNAs play a key role in prokaryotic gene regulation by influencing translation and mRNA stability.
What is antisense RNA?
Antisense RNA is RNA transcribed from the strand of DNA opposite the template strand, which is complementary to the mRNA.
How does antisense RNA inhibit translation?
Antisense RNA can inhibit translation by base pairing with the sense strand of mRNA, preventing ribosome binding or translation initiation.
Can antisense RNA lead to mRNA degradation?
Yes, antisense RNA can lead to mRNA degradation by forming double-stranded RNA, which is recognized by RNases for cleavage.
How can antisense RNA affect transcription
Antisense RNA may interfere with the transcription of the sense gene by base pairing with the mRNA, preventing transcription elongation or initiation.
What is the general mechanism of antisense RNA in gene regulation?
Antisense RNA regulates gene expression by base pairing with the sense mRNA, either inhibiting translation, promoting degradation, or blocking transcription.
What is the relationship between sense and antisense RNA?
Sense RNA is the mRNA produced by transcription of the gene’s coding strand, while antisense RNA is the complementary RNA transcribed from the opposite strand, which can regulate gene expression.
Can antisense RNA inhibit both translation and transcription?
Yes, antisense RNA can inhibit both translation (by base-pairing with mRNA) and transcription (by interfering with gene transcription).
