Molecular Genetics FINAL .EXAM
During attenuation, when tryptophan levels are high, the __________ stem-loop forms and transcription __________ the trpL gene.
3-4 ends just past
What is an operon?
A group of genes under the control of a single promoter.
Why is feedback inhibition an advantage to a bacterium?
Feedback inhibition prevents a bacterium from overproducing the product of a metabolic pathway.
What is an advantage of gene regulation?
Gene regulation enhances efficiency in terms of energy use. A cell does not waste energy making RNAs and proteins it does not need.
What type of bonding interaction causes stem-loops to form?
Hydrogen bonding between complementary regions of the RNA transcribed from the beginning of the trp operon causes stem-loops to form
Which data provides the strongest evidence that O1 is not the only operator site?
The data for the cases in which O2 and O3 are deleted indicate that O1, by itself, is not the only lac operator site.
Which genes are under the control of the lac promoter?
The lacZ, lacY, and lacA genes are under the control of the lac promoter.
How does micF antisense RNA affect the translation of ompF mRNA?
The micF antisense RNA binds to the ompF mRNA and inhibits its translation.
Explain how the presence of tryptophan favors the formation of the 3-4 stem loop.
The presence of tryptophan causes the trpL gene to be translated up to its stop codon. This blocks region 2 from hydrogen bonding with any other region, which allows a 3-4 step-loop to form. The 3-4 stem-loop causes transcriptional termination.
Why is it beneficial for the bacterium to regulate the lac operon with both a repressor protein and an activator protein?
The repressor protein allows the cell to avoid turning on the operon in the absence of lactose. The activator protein allows the cell to choose between glucose and lactose.
Under what conditions is lac repressor bound o the lac operon?
This repressor protein is bound to the lac operon when allolactose is not bound to the repressor, which occurs when lactose is not available.
At which level is the regulation of gene expression the most energy-efficient?
Transcriptional regulation is the most energy-efficient way to regulate a gene, because a cell avoids wasting energy making RNA or proteins that aren't needed
How does tryptophan affect the function of the trp repressor?
Tryptophan acts as a corepressor that causes trp repressor to bind to the trp operon and repress transcription.
Which of the following combinations will cause the rate of transcription to increase? a) A repressor plus an inducer b) A repressor plus a corepressor c) An activator plus an inhibitor d) None of the above
a) A repressor plus an inducer
Operons involved with the biosynthesis of molecules, such as amino acids, are most likely to be regulated in which of the following manners? a) The product of the biosynthetic pathway represses transcription b) The product of the biosynthetic pathway activates transcription
a) The product of the biosynthetic pathway represses transcription
The binding of __________ to lac repressor causes lac repressor to __________ to the operator site, thereby __________ transcription.
allolactose not bind increasing
When tryptophan binds to the trp repressor, this causes trp repressor to __________ to the trp operator and __________ transcription.
bind inhibit
How does exposing an E.coli cell to glucose affect the regulation of the lac operon via CAP?
cAMP does not bind to CAP and transcription is decreased
An example of a posttranslational covalent modification that may affect protein function is __________.
phosphorylation, acetylation, or methylation
A repressor is a __________ that __________ transcription.
regulatory protein; inhibits
Translation can be regulated by __________.
translational repressors & antisense RNA