test 2 material Flashcards
The lac operon is expressed when
glucose is high and lactose is present
When in a complex with ________, the CAP protein binds to the CAP site and ________ the expression of the lac operon.
cAMP; switches on
In the absence of lactose, the lac repressor is
active and can bind to the operator
The inducer of the lac operon is an isomer of lactose.
t/f
true
When RNA polymerase is bound to the lac promoter sequence, transcription of the lac operon is on.
t/f
true
The trp operon consists of ________ structural genes.
5
In the absence of tryptophan, the trp repressor is
inactive and cannot bind to the operator.
In the presence of tryptophan, tryptophan binds to the
trp repressor
In the presence of tryptophan, transcription of the trp operon is on.
t/f
false (it is on)
An operon is a group of genes that is under the control of a single operator site.
t/f
true
- Cells of an E. coli strain that are trp- lac Z- met+ bio+ were mixed with cells of an E. coli strain that are trp+ lac Z+ met- bio- and cultured for several hours. The cells were removed, washed, and transferred to minimal media containing lactose as the only sugar source. A few cells were able to grow on minimal media with lactose, and formed colonies. How did these
few cells become trp+ lac Z+ met+ bio+ ?
conjugation
How many lac Z genes were present in the cells described in the previous problem (11) that were able to grow on minimal media?
Two, the lac Z- allele on the bacterial chromosome and the lac Z+ allele on the F’ episome.
How would you describe the regulation of lactose metabolism in the cells described in problem 11 that were able to grow on minimal media with lactose as a nutrient?
normal regulation of lactose metabolism.
An E. coli strain that is lac Z is conjugated with E. coli cells carrying an F’ plasmid with the plac Oc lac Z DNA sequence on the episome. The Oc is a mutation of the lactose operator that is no longer able to bind the lac I gene product which codes for the lac repressor. How would the expression of the lac Z be regulated in the resulting cells that are diploid for the lactose regulatory region and the lac Z gene?
constitutive expression of lac Z+.
Predict the phenotype of a lacI mutant.
The lac genes would be expressed continuously.
Predict the phenotype of a lacI S or “super-repressor” mutant. A lacI S mutant synthesizes a repressor that cannot bind to the inducer.
The lac genes would never be expressed efficiently.
If a second wild type or normal copy of the lacI gene (just lacI and not lacZ, lacY, or lacA) is introduced into the lacI mutant cell, what would be the phenotype of this partial diploid (also referred to as a merodiploid)?
The lac genes would be expressed efficiently only in the presence of lactose.
Predict how a lacI S mutant would be affected by the construction of a merodiploid that has a second normal copy of the lacI gene.
The lac genes would never be expressed efficiently.
Predict the phenotype of an operator mutant (Oc) which would prevent the binding of the repressor.
The lac genes would be expressed continuously.
Predict the phenotype of a promoter mutant (lacP) which has a mutation in the promoter for the lac operon.
The lac genes would never be expressed efficiently.
Predict the phenotype of a lacZ mutant, which has a mutation in the gene for β-galactosidase.
The production of β-galactosidase would be affected, but other protein products would be unaffected.
Predict the phenotype of a lacY mutant, which has a mutation in the gene for lactose permease.
The lac genes would be expressed efficiently until the lactose supply in the cell is exhausted.
DNA transformation involves the transfer of DNA via
naked DNA in solution
When DNA from an ampicillin resistant organism is brought into an ampicillin sensitive organism by transformation and the product is grown on agar containing ampicillin
only the transformed cells will grow
In transformation, both strands of donor DNA enter the recipient cell.
t/f
true
Donor DNA is combined with recipient DNA by homologous recombination.
t/f
true
A bacterial cell that is able to take up naked DNA is said to be
competent
Which of these describes a similarity between the lac and ara operons?
A) Expression of structural genes does not occur at high glucose concentrations.
B) lacI and araI both encode trans acting factors.
C) Binding of a regulatory protein is prevented in the presence of an inducer.
D) Allofthesearesimilarities.
E) None of these are similarities.
Expression of structural genes does not occur at high glucose concentrations.
Attenuation of the trp operon:
Occurs in the presence of high levels of tryptophan.
a prophage is
phage DNA integrated into host cell genome
CAP contains an “activating region” that has been proposed to participate in direct protein-protein interactions with RNA polymerase and/or other basal transcription factors.
in all Catabolite-Sensitive Operons
Transcriptional Regulation during the development of a typical large DNA phage the ________________ products are responsible for regulation the transcription (turn on or off the transcription of other genes)
regulatory cascade
In specialized transduction
requires a phage that uses the lysogenic cycle for reproduction AND only certain bacterial genes can be transferred and these genes, as you will see, must exist on either side of the prophage
When the defective phage enters a new bacterial cell
both phage DNA and bacterial DNA integrate into the chromosome of the new cell host
In the process of specialized transduction
only a few specific genes from one bacterial cell are transferred to the second bacterial host by a
phage
In specialized transduction
only bacterial genes near the site of integration of the phage DNA can be transduced
In insertional inactivation
if foreign DNA is inserted, the beta galactosidase marker is inactivated, and the colonies remain white
The lac z gene marker codes for
beta galactosidase, which splits x-gal
When foreign DNA and plasmid are both cut with the same restriction enzyme and mixed together, all molecules will form recombinants.
t/f
false
When beta galactosidase cleaves x-gal, white colonies result.
t/f
false (blue)
