genetics ch.14
During attenuation, when tryptophan levels are high, the _____ stem-loop forms and transcription ______ the trpL gene.
3-4/ends just past
A gene which is usually turned down but can be activated is under negative control. A) True B) False
A
Catabolite repression requires an inducer and an activator protein. A) True B) False
A
How might antisense RNA affect translation? A) It can interfere with ribosome binding by blocking binding sites. B) It can enhance ribosome binding by modifying binding sites. C) It can prevent identification of the start codon by the ribosome. D) It can interfere with the normal secondary structure of the mRNA molecule.
A
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 C. A precursor of the biosynthetic pathway represses transcription D. A precursor of the biosynthetic pathway activates transcription
A
The most convincing evidence that lacI is a diffusible protein is: A) A merozygote with only one functional lacI gene is able to regulate both copies of the lac operon. B) A merozygote with only one functional lacO is unable to regulate both copies of the lac operon. C) The lacI gene is located very close to the lac operon. D) Mutants lacking lacI function do not respond to changes in lactose concentration. E) All of the above.
A
Which of the following conditions would cause transcription to be activated? A. a repressor plus an inducer B. a repressor plus a corepressor C. an activator plus an inhibitor D. none of the above
A
Which of the following would you expect to find in an inducible system? A) A repressor protein, which is bound to DNA in absence of any other factor. B) A repressor protein, which is bound to DNA in the presence of a corepressor. C) An activator protein, which is bound to DNA in absence of any other factor. D) An activator protein, which is bound to DNA only in the absence of an inhibitor.
A
Why does the ribosome stall on region 1 during attenuation? A) Translation of this region requires tRNAtrp. B) High levels of tryptophan interfere with ribosome function. C) Low levels of tryptophan lead to intrinsic termination. D) Binding of the repressor protein prevents further translation.
A
What is a operon?
A group of genes under the control of a single promotor.
Give two lines of evidence that indicate the lac operon is inducible
Addition of lactose to the culture medium dramatically increases the levels of lactose utilization enzyme expression: removal of lactose leads to an abrupt termination of expression of these enzymes: mutations that allow constitutive expression of these enzymes exist
What is the main difference between an activator protein and an inducer?
An activator protein is a protein that can bind directly to DNA. An inducer is a small molecule which either binds a regulatory protein and prevents it from binding DNA or binds to an activator protein and allows it to bind DNA.
A translational regulatory protein: A) Binds to DNA and prevents translation. B) Binds to mRNA and prevents translation. C) Binds to rRNA and prevents translation. D) Binds to tRNA and prevents translation.
B
All of the genes involved in functioning of the lac operon are inducible. A) True B) False
B
If regulation of a gene involves a repressor protein, it is an inducible gene. A) True B) False
B
If the addition of lactose was accidentally omitted, how would the results have been affected? A) There would have been no effect on the results. B) In the mated strain, there would have been less than 1% β-galactosidase activity rather than 220%. C) In the original mutant strain, there would have been less than 1% β-galactosidase activity instead of 100%. D) In the mated strain, there would have been 100% β-galactosidase activity instead of 220%.
B
On its chromosome, an E.Coli cell is lacl- lacZ+ lacY+ lacA+. What is the expected level of expression of the lac operon genes (lacZ+ lacY+ lacA+) in the absence of lactose? A. both lac operons would be expressed B. neither lac operon would be expressed C. only the chromosomal lac operon would be expressed D. only the lac operon on the F' factor would be expressed
B
The inducer for the lac operon is: A) lactose B) allolactose C) β-galactosidase D) galactose
B
The lac repressor protein can repress the operon by binding to any one of the three binding sites in the operator. A) True B) False
B
Transcriptional regulation: A) Is highly efficient at completely preventing transcription. B) Allows the cell to only produce proteins that are needed at the time. C) Can be induced by a repressor protein. D) All of these. E) None of these.
B
Which of the following genes is not a structural gene of the lac operon? A) lacA B) lacI C) lacY D) lacZ
B
Attenuation of the trp operon: A) Occurs when transcription is complete before translation begins. B) Is mediated by the trp repressor protein. C) Occurs in the presence of high levels of tryptophan. D) All of the above. E) None of the above.
C
If the original mutation that caused constitutive expression had been in the operator site instead of the lacI gene, how would the results have been affected? A) There would have been no effect on the results. B) In the mated strain, there would have been 220% β-galactosidase activity in the absence of lactose. C) In the mated strain, there would have been 100% β-galactosidase activity in the absence of lactose. D) In the original mutant strain, there would have been < 1% β-galactosidase activity in the absence of lactose.
C
The purpose of the sonication step is to A) Stop conjugation B) Hydrolyze β-ONPG C) Break open the bacterial cells D) Denature the F factor
C
What effect would you expect if gene expression of the lac operon were completely repressed? A) The cell would be more efficient without "wasting" the energy required for the low level of lacZ, lacY, and lacA gene expression. B) Allolactose would accumulate within the cell and become toxic. C) Lactose would not be converted into the inducer and the operon could not be induced. D) All of these. E) A and B only.
C
What is the best explanation for the stem loop arrangement seen in the absence of translation of the trpL gene? A) Region 4 binds to region 3 before region 2 has been transcribed. B) Region 1 is unable to bind to region 3 or 4. C) The 1:2 stem loop has more base pairs than a 2:3 stem loop. D) The ribosome prevents region 1 from binding to any other region.
C
Which of the following elements, when nonfunctional, would lead to a reduction in the total amount of functional lacZ produced by a bacterial cell? A) The operator. B) The lacI gene. C) The CAP site. D) The lacA gene. E) The lacY gene.
C
Genes within an operon: A) Tend to be regulated by a common regulatory mechanism. B) Are generally involved in the same biochemical pathway. C) Are expressed as a polycistronic RNA. D) All of the above. E) None of the above.
D
If β-ONPG was accidentally omitted from this experiment, how would the results have been affected? A) There would have been no effect on the results. B) There would have been yellow color in all four tubes. C) There would have been yellow color in the first two tubes only. D) There would not have been yellow color in any of the four tubes.
D
The absence or presence of lactose has no effect on the original mutant strain because A) It already makes a large amount of lactose. B) It cannot transcribe the operon under any conditions. C) The operator site is defective. D) The repressor protein is defective.
D
Which of the following would be an example of enzyme adaptation? A) Enzymes required for glucose utilization are constitutively expressed. B) Addition of phosphate groups to a protein can activate it. C) Certain enzymes are made up of multiple subunits. D) Enzymes for tryptophan synthesis are not made in the presence of tryptophan.
D
An allosteric enzyme: A) Has two different binding sites. B) Is regulated by binding of a regulatory molecule somewhere other than the active site. C) May be regulated by feedback inhibition. D) Is an example of posttranslational regulation. E) All of these.
E
An example of a posttranslational covalent modification that may regulate protein function is
Phosphorylation, acetylation, and methylation
Which point of regulation would a bacterium be most likely to use if an important goal was quick production of functional protein?
Posttranslation.
Describe enzyme adaptation.
Production of the enzyme only occurs when substrate becomes available, and stops when the supply of substrate is exhausted.
Would you expect repression or attenuation of the trp operon to be a more efficient method?
Repression, because attenuation requires transcription and translation of the trpL sequence.
How many ribosomes are required for synthesis of the trp structural genes?
Two, one to prevent attenuation and one to translate the structural genes.
What advantage does diauxic growth present for a bacterium?
Utilization of glucose with constitutively active enzymes is preferred over utilization of other sugars which require specialized enzymes. This is expected to be more efficient for the bacterium.
The binding of _____ to the lac repressor causes the lac repressor to _____ to the operator site, thereby ______ transcription.
allolactose, not bind, increasing
When tryptophan binds to the trp repressor, this causes the 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
For a riboswitch that controls transcription, the binding of a small molecule such as TPP controls whether the RNA
has an anti-terminator or terminator stem-loop
A repressor is a _______ that ______ transcription.
regulatory protein / inhibits
Translation can be regulated by
translational repressors and antisense RNA
List two examples of metabolic proteins regulated by bacteria.
tructural genes of the lac, trp, or ara operons
