Transference of genetic information and E. coli operons Practice exam 2

Question 1

The lac operon is expressed when

Answer 1

glucose is low and lactose is present

Question 2

When in 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

True or False: The inducer of the lac operon is an isomer of lactose.

Answer 4

True

Question 5

True or False: When RNA polymerase is bound to the lac promoter sequence, transcription of the lac operon is on

Answer 5

True

Question 6

The Trp operon consists of __ structural genes.

Answer 6

Five

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

True or False: In the presence of tryptophan, transcription of the trip operon is on.

Answer 9

False

Question 10

True or False: An operon is a group of genes that is under the control of a single operator site

Answer 10

True

Question 11

Cells of an E. coli strain that are trap- lacZ- met+ bio+ were mixed with cells of an E. coli strain that are trap +lacZ+met -bio- and cultured for several hours. Then cells were removed, washed, and transferred to minimal containing media lactose as the only sugar source. A few cells were able to grow on minimal media with lactose, and formed colonies . How’d these cells become trp+ lacZ+ met+ bio+.

Answer 11

conjugation

Question 12

An E. coli strain is F+ lacZ- met + bio+. Cells from this strain are mixed with an E. coli strain that is lacZ+ met- bio- and carrying an F+ episome with the p(lac) O+lacZ+ DNA sequence on the episome, and cultured for several hours . Then 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 were these few cells able to become lacZ+ did+ met+ bio+?

Answer 12

conjugation

Question 13

How many lac Z genes were present in the cells described below able to grow on minimal media? Cells of an E. coli strain that are trap- lacZ- met+ bio+ were mixed with cells of an E. coli strain that are trap +lacZ+met -bio- and cultured for several hours. Then cells were removed, washed, and transferred to minimal containing media lactose as the only sugar source. A few cells were able to grow on minimal media with lactose, and formed colonies. How many will grow?

Answer 13

Only 1, the lac Z+ allele on the bacterial chromosome

Question 14

An E. coli strain that is lacks conjugated with E. coli cells carrying an F+ plasmid with the plac Oc lacZ DNA sequence on the episome. The Oc is a mutation of the lactose operator that is no longer able to bind the lacI gene product which codes for the lactose regulatory region and the lac Z gene?

Answer 14

Constitutive expression of lac Z+

Question 15

DNA transformation involves the transfer of DNA via

Answer 15

Naked DNA in solution

Question 16

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, what happens?

Answer 16

Only the transformed cells will grow

Question 17

True or False: In transformation, both strands of donor DNA enter the recipient cells.

Answer 17

False

Question 18

True or False: Donor DNA is combined with recipient DNA by homologous recombination.

Answer 18

True

Question 19

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

Answer 19

competent

Question 20

What describes a similarity between the lac and ara operons is said to be

Answer 20

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

Question 21

Attenuation of the trip operon

Answer 21

Occurs in the presence of high levels of tryptophan

Question 22

A prophage is a

Answer 22

phage DNA integrated into the host cell genome

Question 23

Review Table

Answer 23

Review Table

Question 24

Predict the phenotype of a lacI mutant

Answer 24

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

Question 25

If a second wildtype or normal copy of the of the lacI gene (just lacI and not LacZ,LazY, or LacA) is introduced into the lacI mutant cell, what would be phenotype of this partial diploid (also reffered to as a merodiploid)?

Answer 25

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

Question 26

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 26

The lac genes would never be expressed efficently

Question 27

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

Answer 27

The lac genes would be expressed continuously