Concept of Genetics Ch. 16
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 merozygote with only one functional lacI gene is able to regulate both copies of the lac operon.
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 repressor protein, which is bound to DNA in absence of any other factor.
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.
All of the above
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.
All of these.
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.
Allows the cell to only produce proteins that are needed at the time.
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.
Binds to mRNA and prevents translation.
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.
Enzymes for tryptophan synthesis are not made in the presence of tryptophan.
All of the genes involved in functioning of the lac operon are inducible. A) True B) False
False
If regulation of a gene involves a repressor protein, it is an inducible gene. A) True B) False
False
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
False
The genes required for the breakdown of cellobiose are likely to be I by cellobiose, and the genes required for the synthesis of isoleucine are expected to be II by isoleucine. a. I = induced ; II = repressed b. I = induced ; II = induced c. I = repressed ; II = induced d. I = repressed ; II = repressed
I = induced ; II = repressed
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.
It can interfere with ribosome binding by blocking binding sites.
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.
Lactose would not be converted into the inducer and the operon could not be induced.
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.
Occurs in the presence of high levels of tryptophan
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.
The 1:2 stem loop has more base pairs than a 2:3 stem loop.
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.
The CAP site
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.
Translation of this region requires tRNAtrp.
A gene which is usually turned down but can be activated is under negative control. A) True B) False
True
Catabolite repression requires an inducer and an activator protein. A) True B) False
True
The presence of tryptophan does what to the trp repressor? a. inactivates it b. activates it c. degrades it d. initiates transcription of e. none of the above
activates it
The inducer for the lac operon is: A) lactose B) allolactose C) beta-galactosidase D) galactose
allolactose
An enzyme that contains both a catalytic site and a regulatory site is called _______. a. antisense b. inducible c. allosteric d. cis-acting
allosteric
A mutation in the lac repressor protein that prevents it from binding to allolactose will cause which of the following? Assume that glucose is not present. a. expression of the lacZ gene to be constitutively high b. expression of the lacZ gene to be constitutively low c. expression of the lacZ gene to be high in the presence of lactose and low in the absence of lactose d. expression of the lacZ gene to be low in the presence of lactose and high in the absence of lactose
expression of the lacZ gene to be constitutively low
The lac operon is turned off in the presence of what? a. lactose b. glucose c. arabinose d. any sugar
glucose
Riboswitches have been found in all of the following organisms EXCEPT a. archaea. b. bacteria. c. fungi. d. plants. e. humans
humans
Which of the following genes is not a structural gene of the lac operon? A) lacA B) lacI C) lacY D) lacZ
lacI
The lac repressor protein binds to the ________ site. a. CAP b. terminator c. promoter d. silencer e. operator
operator
Feedback inhibition is a mechanism to regulate gene expression at the ________ level. a. transcriptional b. posttranscriptional c. translational d. posttranslational
postranslational
Cyclic AMP is involved in the regulation of which of the following bacterial operons? a. the lac operon b. the trp operon c. Both A and B d. Neither A nor B
the lac operon
The ______ operon utilizes attenuation as a regulatory mechanism. a. the lac operon b. the trp operon c. Both A and B d. Neither A nor B
the trp operon