BIOL 367 Lecture Notes - Lecture 6: Phenylalanine, Tryptophan, Lac Operon

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30 Nov 2014

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1-the regulatory region of the tryptophan operon has been used to replace the promoter and regulatory information of the lacz gene. That is the lacz gene is now expressed as if it were the tryptophan operon. What would the levels of b -galactosidase expression be when the following strains are grown in the media indicated. Note: assume that attenuation accounts for a ten fold regulation and that the trp repressor protein accounts for about 70 fold regulation. Also assume that wild type cells express a maximum of about. Galactosidase: a mutation in the ribosome binding site of the leader peptide would produce. ________ units of b -galactosidase in mimimal medium without tryptophan: a mutation that deleted region three of the leader sequence would produce. ________ units of b -galactosidase in mimimal medium and lots of tryptophan. ________ units of b -galactosidase in mimimal medium without tryptophan: a mutation that replaces the two trp codons by phenylalanine codons*

Related Questions

The following test deals with the regulation of the trp operon of Escherichia coli. Two mutants of this operon are described: in mutant A, the operator region of the operon carries a point mutation so that it is unable to carry out its function; mutant B expresses a trp repressor protein unable to bind tryptophan. Review the principle of the regulation of this operon and then solve the following questions related to the behavior of the mutant cells using the options below.

A: Mutant A B: Mutant B C: Both of them D: Neither of them

a) _____ In the presence of tryptophan these cells behave like wild-type cells. b) _____ In the absence of tryptophan these cells behave like wild-type cells. c) _____ These cells are able to synthesize tryptophan.
d) _____ These cells are able to break down tryptophan.

e) _____ Tryptophan is able to act as an inducer in these cells.
f) _____ Tryptophan is able to act as a corepressor in these cells.
g) _____ The structural genes of the trp operon can be transcribed in these cells.
h) _____ In the presence of tryptophan RNA polymerase binds to the promoter of the trp operon in these cells.
i) _____ In the absence of tryptophan RNA polymerase binds to the promoter of the trp operon in these cells.
j) _____ These cells die if tryptophan is omitted from their medium.
k) _____ These mutants can be ââcuredââ by expressing wild-type trp repressor in them.
l) _____ These mutants can be ââcuredââ by transforming them with a wild-type trp operator.

please answer all the questions answering only one question is not helpful!
Question 1

0 / 1 pts

Which of the following E. coli strains with the lac genotypes will synthesize beta-galactosidase in the presence of lactose?

Note: Superscript wouldn't work in the answers, so for example, lacIs means lacI^s(superrepressor of lacI)

lacIâ lacPâ lacOâ lacZâ lacYâ

lacIs lacP+ lacO+ lacZ+ lacYâ / lacI+ lacP+ lacO+ lacZâ lacY+

lacIs lacPâ lacO+ lacZâ lacY+ / lacI+ lacP+ lacO+ lacZ+ lacY+

lacIâ lacPâ lacO+ lacZ+ lacY+

lacI+ lacP+ lacO+ lacZ+ lacY+

Question 2

0 / 1 pts

Some mutations in the trp 5' UTR region increase termination by the attenuator. An example of a mutation that may have this effect is a

Choose the best answer!

mutation that changes the bases in region 3 of the 5' UTR, such that they no longer pair with region 2 or 4.

deletion of the two tryptophan codons in the 5' UTR leader peptide.

deletion in region 2 in the 5' UTR that prevents it from pairing with region 3.

The second and third answers are correct.

The first, second, and third answers are correct.

IncorrectQuestion 3

0 / 1 pts

Several examples of antisense RNA regulating translation in bacterial cells have been discovered. If you wanted to design a construct to artificially control translation of a bacterial gene with antisense RNA, what type of sequences should the antisense RNA contain?

A sequence complementary to the operator of an operon.

A sequence complementary to a 5' UTR.

A sequence complementary to the Shine-Dalgarno site of the mRNA.

The first and second choices are correct.

The second and third choices are correct.

Question 4

0 / 1 pts

Which of the following correctly describes the function of microRNAs?

Choose the best answer.

MicroRNAs are encoded by genes in the genome of an organism.

MicroRNAs form mRNA which encodes a protein repressor for another gene.

MicroRNAs encode a mRNA that base pairs with itself, forming double stranded RNA.

MicroRNAs are cut into small pieces, then bound by the complex of proteins called RISC to repress the translation of other mRNAs in the cell.

The first and second answers are correct.

The first, third, and fourth answers are correct.

The third and fourth answers are correct.

whitemole409

18) In your research on gene regulation in E. coli, you produce 2 mutant strains with the same phenotype: they can grow on lactose but not on glucose. To investigate these 2 mutants further, you perform a complementation test using them and discover that the diploid combination strain can grow on glucose or lactose. From this, you can deduce that:

a.)Both mutants have a mutation in the same gene

b.)The 2 mutants have mutations in different genes
c.)Glucose and lactose metabolic pathways in E. coli utilize at least one shared gene in common
d.)At least 2 different genes are required for glucose metabolism in E. coli
e.) b) and d)

19. In your research on the lac operon, you produce a unique regulatory mutatant strain of E. Coli where the lac l gene's repressor protein binding site for the operator is normal (wild-type) but its lactose binding site no longer binds lactose. The expected phenotype of this mutant will be:

a. inability to grow on lactose only medium

b. ability to grow on lactose only medium

c. blue colony color when grown on glycerol plus x-gal medium

d. blue colony oclor when grown on lactose plus x-gal medium

e. b & d

20.

20) In your research on the lac operon, you create a diploid E.coli strain with the following genotype (+) = wild type gene, (-) = mutant gene.

I- /O+ /Z- /Y+

I+ /Oc /Z+ /Y+
Can this diploid mutant grow on medium containing lactose as the only carbon source?

a) Yes

b) No

c) Maybe, it depends on if the Oc mutation is dominant or recessive

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BIOL 367 Lecture Notes - Lecture 6: Phenylalanine, Tryptophan, Lac Operon

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