BSCI 222 Study Guide - Midterm Guide: Operon, Repressor, Corepressor

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limebee726

1 Oct 2015

School

University of Maryland

Department

Biological Sciences Program

Course

BSCI 222

Professor

Dr.Straney

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Document Summary

Gss worksheet: briefly describe how the trp operon works, and how attenuation affects the trp operon as well. The trp operon is a negative repressible operon; this means that the regulatory protein is a repressor, and that the operon is usually on and something will cause it to be turned off. The repressor is continually made in its inactive form, and it will be activated by its associated co-repressor, tryptophan. When tryptophan levels are high, it binds to the repressor (thereby activating it), the repressor binds to the operator, and transcription of the structural genes that code for tryptophan is terminated. Rna polymerase continues with transcription of the 5" utr (and eventually the trp structural genes). Regions 1+2 and regions 3+4 will be free to form the terminator hairpin loops, and transcription will be terminated: deletions in region 2 of the mrna 5" utr.

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.

1. What is the term when the product of a biochemical pathway inhibits the activity of the first enzyme of a pathway?

		feedback inhibition.
		activator inhibition.
		diffusional regulation.
		enzyme activation.

2. Through control of gene expression, prokaryotes respond to changing __________ conditions.

		internal
		protein
		environmental
		genetic

3. A protein that negatively regulates transcription by binding to the operator is known as the

		operon
		repressor
		activator
		inducer

4. During attenutation, when tryptophan levels are high, the ________ stem-loop forms and transcription ________ the trpL gene.

		1-2, ends just past
		3-4, ends just past
		1-2, continues beyond
		3-4, continues beyond

5. The process of turning on the expression of a gene in response to a substance in the environment is called:

		constituation.
		repression.
		induction.
		catabolism.

6. What is a function of some specific transcription factors?

		to bind to the promoter region of the gene to facilitate the proper alignment of the RNA polymerase
		to bind to the centromere to induce meiosis
		to bind to enhancer regions to help regulate gene transcription
		to bind to the operator to recruit sigma factor

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

		cAMP binds to CAP and transcription is increased.
		cAMP binds to CAP and transcription is decreased.
		cAMP does not bind to CAP and transcription is increased.
		cAMP does not bind to CAP and transcription is decreased.

8. The lac repressor protein works when mutations in the repressor gene and structural genes are:

		in cis or in trans.
		in trans only.
		in cis only.
		in both prokaryotes and eukaryotes.

scarletwombat949

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.

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BSCI 222 Study Guide - Midterm Guide: Operon, Repressor, Corepressor

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