BIOL308 Lecture Notes - Lecture 6: Lac Operon, Catabolite Repression, Repressor

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lemonclam177

14 Feb 2018

School

University of Waterloo

Department

Biology

Course

BIOL308

Professor

Dragana Miskovic

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Document Summary

You have discovered base changes in the promoter region of the operon in a bacterial chromosome. Regulator can execute positive or negative regulation. Dna bending consequence of trans factor binding, can be positive or negative. Dna looping direct contact can be achieved even when promoter and: define constitutive and regulated proteins. Helix-turn helix: apart from the dna binding domain, we have mentioned other two domains found in prokaryotic binding proteins. What are they: enhancer binding domain, ogliodimerization domain (dimerization domain, thinking question: three adjacent genes are involved in arginine biosynthesis. (they are structural genes of arginine operon. ) You have three dna fragments, each containing coding sequence for one of these three structural genes, and you have used these fragments to make three different probes for northern blotting (one probe for each of the three genes). You have isolated mrna from bacteria and you have performed the agarose gel electrophoresis followed by northern blotting.

Related Questions

a. Suppose you isolated a mutation in the CRP gene that results in the production of a CRP protein that cannot bind cAMP. What effect would such a mutation have on expression of the lac operon in the presence versus the absence of lactose (assume that glucose is absent in both cases)?

Answer:

b. Suppose you isolated a different mutation in the CRP gene that results in the production of a CRP protein that binds to the CRP-binding site in the lac promoter even when there is no cAMP available. What effect would this mutation have on expression of the lac operon in the presence versus the absence of lactose, if glucose were also available in both cases?

Answer:

Regulation of Gene Expression Question. Help with regulatory proteins (operators) and protein binding sites!!

1. In studying the bacterial the srp operon, you have isolated two different mutants (con1 and con2) that cause constitutive expression of the srp operon (constitutive expression of srp1 and srp2). One of the mutants has a mutation in a DNA binding site (e.g. operator), and the other has a loss-of-function mutation in the gene that encodes a protein that binds to the DNA binding site (e.g. repressor protein).

You perform an analysis using partial diploids to determine which of the two mutants has a defect in the binding site and which of the two mutants has a mutation in the gene encoding the binding protein.

a. Assuming you can assay levels of the two Srp proteins, what results do you predict for the two strains (i and ii below) if con2 encodes the regulatory protein and con1 is the regulatory binding site? In predicting results, indicate whether expression of the Srp1 and Srp 2 proteins will be constitutive or inducible (you will circle an answer in the bolded region below). 2 pts

i. (a) con1^-con2⁺srp1^-srp2⁺/ (b) con1⁺con2⁺srp1⁺srp2^-

ii. (a) con1⁺con2^-srp1^-srp2⁺/ (b) con1⁺con2⁺srp1⁺srp2^-

b. What results do you predict for the two strains (i and ii) if con1 encodes the regulatory protein and con2 is the regulatory binding site? 2 pts

Answer for a(i) (circle either constitutive or inducible for each gene):

srp1 constitutive / inducible

srp2 constitutive / inducible

Answer for a(ii) (circle either constitutive or inducible for each gene):

srp1 constitutive / inducible

srp2 constitutive / inducible

Answer for b(i) (circle either constitutive or inducible for each gene):

srp1 constitutive / inducible

srp2 constitutive / inducible

Answer for b(ii) (circle either constitutive or inducible for each gene):

srp1 constitutive / inducible

srp2 constitutive / inducible

harlequindeer134

1.) What type of control best describes the lac operon when it is regulated by allolactose? Explain the features of this type of regulation using the lac operon as an example.

2.) What is positive gene regulation?

a) when an activator protein binds to the operator of a gene to turn expression off

b) when a repressor protein binds to the operator of a gene to turn expression off

c) when an activator protein binds to the operator of a gene to turn expression on

d) when a repressor protein binds to the operator of a gene to turn expression on

e) when a protein binds to DNA to change gene expression

3.) In the lactose operon of E. coli, what is the function of each of the following genes or sites: a) regulator, b) operator, c) promoter, d) structural gene Z and e) structural gene Y?

a) regulator gene

b) operator

c) promoter

d) structural gene Z

e) structural gene Y

4.) In a negative, repressible regulatory mechanism, transcription of the structural gene(s) occurs in

a) the presence of the co-repressor, but not in its absence.

b) the absence of the co-repressor, but not in its presence.

c) the presence of the inducer, but not in its absence.

d) the absence of the inducer but not in its presence.

e) the absence or presence of the co-repressor.

What are answers and can you explain them to me?

BIOL308 Lecture Notes - Lecture 6: Lac Operon, Catabolite Repression, Repressor

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