test 2 material

Question 1

The lac operon is expressed when

Answer 1

glucose is high and lactose is present

Question 2

When in a complex with ________, the CAP protein binds to the CAP site and ________ the expression of the lac operon.

Answer 2

cAMP; switches on

Question 3

In the absence of lactose, the lac repressor is

Answer 3

active and can bind to the operator

Question 4

The inducer of the lac operon is an isomer of lactose.

t/f

Answer 4

true

Question 5

When RNA polymerase is bound to the lac promoter sequence, transcription of the lac operon is on.
t/f

Answer 5

true

Question 6

The trp operon consists of ________ structural genes.

Answer 6

5

Question 7

In the absence of tryptophan, the trp repressor is

Answer 7

inactive and cannot bind to the operator.

Question 8

In the presence of tryptophan, tryptophan binds to the

Answer 8

trp repressor

Question 9

In the presence of tryptophan, transcription of the trp operon is on.
t/f

Answer 9

false (it is on)

Question 10

An operon is a group of genes that is under the control of a single operator site.
t/f

Answer 10

true

Question 11

11. 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+ ?

Answer 11

conjugation

Question 12

How many lac Z genes were present in the cells described in the previous problem (11) that were able to grow on minimal media?

Answer 12

Two, the lac Z- allele on the bacterial chromosome and the lac Z+ allele on the F’ episome.

Question 13

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?

Answer 13

normal regulation of lactose metabolism.

Question 14

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?

Answer 14

constitutive expression of lac Z+.

Question 15

Predict the phenotype of a lacI mutant.

Answer 15

The lac genes would be expressed continuously.

Question 16

Predict the phenotype of a lacI S or “super-repressor” mutant. A lacI S mutant synthesizes a repressor that cannot bind to the inducer.

Answer 16

The lac genes would never be expressed efficiently.

Question 17

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)?

Answer 17

The lac genes would be expressed efficiently only in the presence of lactose.

Question 18

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.

Answer 18

The lac genes would never be expressed efficiently.

Question 19

Predict the phenotype of an operator mutant (Oc) which would prevent the binding of the repressor.

Answer 19

The lac genes would be expressed continuously.

Question 20

Predict the phenotype of a promoter mutant (lacP) which has a mutation in the promoter for the lac operon.

Answer 20

The lac genes would never be expressed efficiently.

Question 21

Predict the phenotype of a lacZ mutant, which has a mutation in the gene for β-galactosidase.

Answer 21

The production of β-galactosidase would be affected, but other protein products would be unaffected.

Question 22

Predict the phenotype of a lacY mutant, which has a mutation in the gene for lactose permease.

Answer 22

The lac genes would be expressed efficiently until the lactose supply in the cell is exhausted.

Question 23

DNA transformation involves the transfer of DNA via

Answer 23

naked DNA in solution

Question 24

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

Answer 24

only the transformed cells will grow

Question 25

In transformation, both strands of donor DNA enter the recipient cell.
t/f

Answer 25

true

Question 26

Donor DNA is combined with recipient DNA by homologous recombination.
t/f

Answer 26

true

Question 27

A bacterial cell that is able to take up naked DNA is said to be

Answer 27

competent

Question 28

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.

Answer 28

Expression of structural genes does not occur at high glucose concentrations.

Question 29

Attenuation of the trp operon:

Answer 29

Occurs in the presence of high levels of tryptophan.

Question 30

a prophage is

Answer 30

phage DNA integrated into host cell genome

Question 31

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.

Answer 31

in all Catabolite-Sensitive Operons

Question 32

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)

Answer 32

regulatory cascade

Question 33

In specialized transduction

Answer 33

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

Question 34

When the defective phage enters a new bacterial cell

Answer 34

both phage DNA and bacterial DNA integrate into the chromosome of the new cell host

Question 35

In the process of specialized transduction

Answer 35

only a few specific genes from one bacterial cell are transferred to the second bacterial host by a
phage

Question 36

In specialized transduction

Answer 36

only bacterial genes near the site of integration of the phage DNA can be transduced

Question 37

In insertional inactivation

Answer 37

if foreign DNA is inserted, the beta galactosidase marker is inactivated, and the colonies remain white

Question 38

The lac z gene marker codes for

Answer 38

beta galactosidase, which splits x-gal

Question 39

When foreign DNA and plasmid are both cut with the same restriction enzyme and mixed together, all molecules will form recombinants.
t/f

Answer 39

false

Question 40

When beta galactosidase cleaves x-gal, white colonies result.
t/f

Answer 40

false (blue)