Chapter 16 review
You identify a CAP mutant protein that is constitutively bound to the CAP site. Under which conditions will the lac operon be transcribed at high levels in cells that contain this mutant protein? Check all that apply.
-Lactose and glucose are both present -Lactose is present, glucose is not
Regulation of gene expression may occur at which of the following levels?
-transcription -translation -posttranslation
Transcription of the lac operon results in the production of how many different mRNA transcripts?
1
In a particular E. coli strain, a mutation in the thiMD operon results in improper formation of the stem loop secondary structure making it impossible to bind TPP. There are two enzymes encoded by the thiMD operon. How many of the enzymes encoded in the thiMD operon are translated?
2 -In the TPP riboswitch, transcription is attenuated when TPP is bound, and transcription occurs when TPP is not bound. Therefore, if TPP cannot bind to the mRNA, the operon will be transcribed completely
What stem-loop conformations favor attenuation in the trp operon?
3-4
Attenuation (in operons)
3-4 sten loop forms to terminate transcription, happens when trp is high
operon
A group of two or more genes under the transcriptional control of a single promoter.
repressor
A regulatory protein that binds to the DNA and inhibits transcription
activator
A regulatory protein that increases the rate of transcription.
operator
A sequence of bases that provides a binding site for a repressor protein.
promoter
A sequence of bases that signals the beginning of transcription
inducer
A small effector molecule that causes transcription to increase/deactivates repressor protein
inducer
A specific small molecule that inactivates the repressor in an operon.
In Jacob, Monod, and Pardee's experiment, what would have been the conclusion if all four tubes produced a yellow color when β-ONPG was added?
Expression of the lac operon is constitutive whether lacI is functional or not
When both glucose and lactose are absent, the highest rate of transcription occurs. T/F
F
In the absence of glucose, and in the presence of lactose, allolactose binds to the repressor, allowing RNA polymerase to carry on transcription. T/F
T
The polycistronic mRNA is transcribed from the lac operon when lactose is present in the cell and glucose is not present. T/F
T
If a cell has a mutant lacY gene that produces a non-functional product, which of the following statements is true?
The lac operon cannot be induced because lactose cannot enter the cell.
How would the interpretation of the Jacob, Monod, and Pardee experimental results change if lacO was mutated instead of lacI?
The lac operon has constitutive expression and O has a cis-effect
You identify a CAP protein mutant that is unable to bind cAMP. How will this mutant affect transcription of the lac operon?
The lac operon will never be transcribed at a high rate.
A deletion in an operon removes the promoter. How will that affect the transcript that is produced from the operon?
The transcript will not be produced -The promoter of an operon is where transcription begins. If the promoter sequence is deleted, transcription will not take place.
You identify a strain of bacteria that has a mutated trp operator that cannot bind the repressor. Under what circumstances will the trp operator be transcribed?
The trp operon will be transcribed when levels of tryptophan in the cell are low.
If the Trp codons in the trpL gene were mutated to encode another amino acid, what would the result be?
The trp operon would never be transcribed.
If the stop codon in the trpL gene were mutated to encode an amino acid (rather than a stop codon), what would the result be?
The trp operon would only be transcribed when tryptophan in the cell was low.
The lac repressor protein is active in the absence of lactose within the cell. T/F
True
You repeat the Jacob, Monod, and Pardee experiment. At the end of your experiment all of the tubes are yellow. What mistake did you most likely make?
You added lactose to all of the tubes.
You repeat the Jacob, Monod, and Pardee experiment. At the end of your experiment all of the tubes are colorless. What mistake did you most likely make?
You forgot to add β-ONPG to the tubes.
For enzymes that are controlled by feedback inhibition
a product of the metabolic pathway inhibits the enzyme.
Allosteric regulation is accomplished by
a small molecule that fits into a site on the enzyme that is not the active site.
The lac repressor is inactivated by binding to which of the following?
allolactose
when lactose levels are present (in bacteria/e.coli) (lac operon)
allolactose bind to lac repressor to deactivate it, increasing rate of trancription
how inducer works in negative control
binds to a repressor, prevents DNA from binding, increasing rate of transcription
antisense RNA
binds to mRNA and prevents translation from starting
The lac repressor __________.
binds to the operator and prevents transcription
when glucose levels are abcenst (in bacteria/e.coli) (lac operon)
cAMP is produced. cAMP attaches to CAP, allowing it to bind to DNA. CAP helps RNA polymerase bind to the promoter, resulting in hight lavels of transcription.
If an E. coli cell is exposed to glucose, what happens?
cAMP levels are decreased, which does not allow the CAP protein to bind to its regulatory region.
unregulated genes
constitutive genes, constant level of expression
When glucose is present ____________.
cyclic AMP is low, CAP does not bind to the activator binding site, and transcription is turned off
posttranslational regulation
functional control of proteins but not gene expression
For a riboswitch that controls transcription, the binding of a small molecule such as TPP controls whether the RNA ______________.
has an antiterminator or terminator stem-loop
allolactose
inducer for lac operon
Which of the following best describes regulation of the lac operon?
inducible, under negative and positive control
lac operon
inducible/ pos
lac I role in lac operons
lac I is repressor, in lac operons a repressor will bind to operator to ihibit trancription
CAP affects which operon(s)?
lac operon
when lactose levels are abscent (in bacteria/e.coli) (lac operon)
lac repressor binds to operator, decreasing rate of transcription
The lac repressor binds to what site within the lac operon?
lacO
Which gene is responsible for producing the protein that converts lactose to allolactose?
lacZ
Which of the following is not part of the lac operon?
lacl
mRNA is trancribed in lac operon when
lactose is present and glucose is absent
Translational regulatory proteins recognize specific areas of what molecule?
mRNA
when glucose levels are present (in bacteria/e.coli) (lac operon)
no cAMP is produced. CAP can't bind to to DNA without cAMP, low transcription
trp binds to___ a what is presemt
operator, corepressor
parts of lac operon
promoter, operator, lacZ, lacY, lacA
components of operon
promoterter operator protein-encoding genes (lac Z, Y, A) terminator
negative control
regulated by repressor, inhibits transcription
trp operon
repressible operon
the trp operon is regulated by
repressor
A gene is inducible and under negative control. Which of the following pairs will allow expression of this gene?
repressor + inducer
when trp levels are present (in bacteria/e.coli) (lac operon)
repressor binds to operator, transcription stops
when trp levels are absent (in bacteria/e.coli) (trp operon)
repressor dissociates from the operator, transcription proceeds
Feedback inhibition frequently involves
the inhibition of the first enzyme in the pathway by the final product of the pathway.
The active site of the lac repressor protein is composed of
the protein domain that binds to DNA.
When both glucose and lactose are present ______________.
the transcription rate is very, very low
levels of regulation of gene expression
transcription translation posttranslation
diauxic growth (in an experiment glucose/lactose present, which taken out first)
when glucose an lactoseare present, glucose tken out first, due to catabolite expression
