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

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Flashcards in Transference of genetic information and E. coli operons Practice exam 2 Deck (27):
1

The lac operon is expressed when

glucose is low and lactose is present

2

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

cAMP; switches on

3

In the absence of lactose, the lac repressor is

active and can bind to the operator

4

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

True

5

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

True

6

The Trp operon consists of __ structural genes.

Five

7

In the absence of tryptophan, the Trp repressor is

inactive and cannot bind to the operator

8

In the presence of tryptophan, tryptophan binds to the

trp repressor

9

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

False

10

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

True

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+.

conjugation

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+?

conjugation

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?

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

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?

Constitutive expression of lac Z+

15

DNA transformation involves the transfer of DNA via

Naked DNA in solution

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?

Only the transformed cells will grow

17

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

False

18

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

True

19

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

competent

20

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

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

21

Attenuation of the trip operon

Occurs in the presence of high levels of tryptophan

22

A prophage is a

phage DNA integrated into the host cell genome

23

Review Table

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Review Table

24

Predict the phenotype of a lacI mutant

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

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)?

Q image thumb

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

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

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The lac genes would never be expressed efficently 

27

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

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The lac genes would be expressed continuously