Deck 7: Operons: Fine Control of Bacterial Transcription

Question 1

________ __________is the enzyme needed to bring lactose into the bacterial cell.

Answer 1

Galactoside permease

Question 2

Which of the following would be effective in blocking transcription from the lac operon in the presence of permease?

A)antibody to RNA polymerase
B)antibody to the repressor protein
C)mutation in the operator
D)an antibody to $\beta$ -galactosidase
E)both antibody to RNA polymerase and mutation in the operator

Answer 2

antibody to RNA polymerase

Question 3

Which of the following bond creates the linkage between glucose and galactose?

A)a glycoside bind.
B)The linkage is through $\beta$ -1,4 bond.
C)It can be broken by $\beta$ -galactosidase.
D)It is a covalent bond.
E)All of the choices are correct.

Answer 3

All of the choices are correct.

Question 4

Which of the following techniques is most useful in determining if RNA polymerase has initiated transcription from the lac DNA template?

A)Southern analysis
B)DNA fingerprinting
C)run-off transcription assay
D)DNA sequencing
E)RACE

Question 5

Which of the following is most likely to occur if the level of glucose is low in a bacterial cell?

A)Cyclic-AMP levels will be depressed.
B)CAP will assist in stimulating transcription of the lac operon.
C)CRP activity will be inhibited.
D)Both Cyclic-AMP levels will be depressed and CRP activity will be inhibited are correct.
E)None of the choices is correct.

Question 6

The ara operon is controlled by the _____________ protein.

Question 7

Which of the following organisms would produce functional lac products in the presence of IPTG?

A)I^s O^c Z^- Y⁺ A⁺
B)I^s O^c Z^- Y^- A^-
C)I⁺ O⁺ Z⁺ Y⁺ A⁺
D)I^-O^c Z⁺ Y⁺ A⁺
E)Both I^s O^c Z^- Y⁺ A⁺ and I^s O^c Z^- Y⁺ A⁺ are correct

Question 8

$\beta$ -galactosidase cleaves the disaccharide lactose into __________ and ____________.

Question 9

The identity of the following molecule is

A)galactose.
B)lactose.
C)glucose.
D)cAMP.
E)heparin.

Question 10

Which of the following is true about the regulation of the trp operon?

A)An aporepressor is involved.
B)A corepressor is involved.
C)Attenuation is one of the mechanism of control.
D)Negative control is involved.
E)All of the choices are true.

Question 11

Which of the following statements is true about a lac operon with this genotype? I^-d O⁺ Z⁺ Y^- A^-

A)The operon is repressible.
B)The operon is nonrepressible.
C)The mutation is cis-dominant.
D)The operon is uninducible.
E)None of the choices is correct.

Question 12

Which of the following is true about the action of CAP at the lac promoter?

A)CAP monomer binds directly to the promoter stimulating polymerase to bind.
B)CAP-AMP blocks recruitment of polymerase to the promoter.
C)CAP blocks the $\alpha$ CTD of RNA polymerase.
D)Binding of the CAP-cAMP to the lac activator-binding site recruits RNA polymerase.
E)CAP monomer binds directly to the promoter stimulating polymerase to bind and CAP blocks the $\alpha$ CTD of RNA polymerase are correct.

Question 13

In the presence of glucose the lac operon is kept inactive by _________ _________.

Question 14

________ is a term used to describe a mechanism in which a protein controls it's own regulation.

Question 15

If an operon is under negative control it means that the operon is never operational.

Question 16

Regions of the 5'-UTRs of mRNAs that alter their structures to control gene expression are called _____________________.

Question 17

Identify the allosteric protein.

A)operator
B)repressor
C)promoter
D) $\beta$ -galactosidase
E)permease

Question 18

In an in vitro transcription assay to detect the level of transcription from a lac operon,one of the RNA precursors was tagged with a fluorescent label on the $\beta$ -phosphate.Which of the following is a likely outcome if transcription occurred?

A)The level of fluorescence would increase along the new RNA strand.
B)Each RNA would have a fluorescent tag on every other nucleotide.
C)The level of fluorescence would be very high in the assay buffer.
D)No fluorescence would be detected in the buffer at the end of the assay.
E)All of the choices are possible.

Question 19

Which of the following is absent in an operon?

A)operator
B)promoter
C)intron
D)both operator and promoter
E)both promoter and intron

Question 20

In the process of creating a trp operon mutant,the region for the riboswitch was accidentally deleted.Which of the following would be a likely observation in the transcription assays?

A)RNA polymerase cannot bind to the promoter.
B)The operon is permanently inhibited.
C)Attenuation would be impaired.
D)Termination would be triggered .
E)The chance of an aptamer binding to the mRNA 5'-UTR increases.

Question 21

Attenuation causes the length of the RNA molecules to be significantly extended.

Question 22

cAMP level is increased by the presence of high levels of glucose.

Question 23

One hypothesis explaining the mechanism of repression of the lac operon states that the repressor binds to the operator and blocks access by the polymerase to the adjacent promoter.

Question 24

The following is an example of a cis-dominant mutation:
I^-d O⁺ Z⁺ Y⁺ A^-

Question 25

Recent experimental evidence has shown that only one operator sequence is needed for maximal expression.

Question 26

Arabinose can derepress the ara operon by causing AraC to loosen its attachment to araO₂ and to bind to araI₂ instead.

Question 27

In the absence of glucose there will be a rapid accumulation of lactose in the following mutant:
I^- O^c Z⁺ Y^-
I^- O⁺ Z⁺ Y^-