Mod 6 Ch. 14

Question 1

A repressor is a ___ that ___ transcription.

Answer 1

Regulatory protein, inhibits

Question 2

Which of the following conditions would cause transcription to be activated?

Answer 2

A repressor plus an inducer

Question 3

What is an operon?

Answer 3

A group of genes under the control of a single promoter

Question 4

The binding of ___ to the lac repressor causes the lac repressor to ___ to the operator site, thereby ___ transcription.

Answer 4

Allalactose, not bind, increasing

Question 5

On its chromosome, an E. coli cell is lacl- lacZ+ lacY+ lacA+. It has an F’ factor that 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?

Answer 5

Neither lac operon would be expressed

Question 6

How does exposing an E. coli cell to glucose affect the regulation of the lac operon via CAP?

Answer 6

cAMP does not bind to CAP and transcription is decreased

Question 7

When tryptophan binds to the trp repressor, this causes the trp repressor to ___ to the trp operator and ___ transcription.

Answer 7

Bind, inhibit

Question 8

During attenuation, when tryptophan levels are high, the ___ step-loop forms and transcription ___ the trpL gene.

Answer 8

3-4, ends just past

Question 9

Operons involved with the biosynthesis of molecules, such as amino acids, are most likely to be regulated in which of the following manners?

Answer 9

The product of the biosynthetic pathway represses transcription

Question 10

Translation can be regulated by..

Answer 10

• translational repressors

- antisense RNA

Question 11

An example of a posttranslational covalent modification that may regulate protein function is ..

Answer 11

Phosphorylation
Acetylation
Methylation

Question 12

For a riboswitch that controls transcription, the binding of a small molecule such as TPP controls whether the RNA..

Answer 12

Has an antiterminator or terminator stem-loop

Question 13

Common points where regulation of gene expression occurs in bacteria.

What is an advantage of gene regulation?

Answer 13

Gene regulation is more efficient. A cell does not waste energy making RNAs and proteins it does not need.

Question 14

Binding sites on a genetic regulatory protein.

Which of these are genetic regulatory proteins and which are small effector molecules?

Answer 14

Activators and repressors are regulatory proteins. Inducers, corepressors, and inhibitors are small effector molecules.

Question 15

Organization of the lac operon and other genes involved with lactose metabolism in E. coli.

Which genes are under the control of the lac promoter?

Answer 15

lacZ, lacY, and lacA genes

Question 16

The cycle of lac operon induction and repression.

Under what conditions is the lac repressor bound to the lac operon?

Answer 16

When it is not exposed to lactose- when allalactose is not bound to the repressor

Question 17

Why is it beneficial for the bacterium to regulate the lac operon with both a repressor protein and an activator protein?

Answer 17

The repressor protein allows the cell to avoid turning on the operon in the absence of lactose. The activator protein allows the cell to choose between glucose and lactose.

Question 18

The identification of three lac operator sites.

Which data provide the strongest evidence that O1 is not the only operator site?

Answer 18

The data in which O2 and O3 are deleted indicate that O1, by itself, is not very strong in repressing the lac operon

Question 19

How does tryptophan affect the function of the trp repressor?

Answer 19

Tryptophan acts as a corepressor that causes the trp repressor to bind to the trp operon and repress transcription

Question 20

Sequence of the trpL mRNA produced during attenuation.

What type of bonding interaction causes the stem-loops to form?

Answer 20

Hydrogen bonding between complementary sequences

Question 21

Explain how the presence of tryptophan favors the formation of the 3-4 stem-loop.

Answer 21

Causes the trpL gene to be translated to its stop codon. This blocks both regions 1 and 2, which allows a 3-4 stem-loop to form. The 3-4 stem-loop causes transcriptional termination.

Question 22

How does micF antisense RNA affect the translation of ompF mRNA?

Answer 22

The micF antisense RNA binds to the ompF mRNA and inhibits its translation

Question 23

Why is feedback inhibition an advantage to the bacterium?

Answer 23

It prevents a bacterium from overproducing the product of a metabolic pathway

Question 24

Which RNA conformation favors transcription?

Answer 24

The RNA conformation with an antiterminator stem-loop favors transcription

Question 25

Which RNA conformation favors translation?

Answer 25

The RNA conformation with the Shine-Dalgarni antisequestor