BIOL 1201 Lecture Notes - Lecture 15: Trp Operon, Operon, Repressor

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23 Nov 2015

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Gene regulation: bacterial genome organization, single, circular chromosome, naked dna, no introns, located in the cytoplasm, plasmids (only has a few genes on it, why regulate, energetics. You don"t make proteins that you don"t need (expensive processes that use up your energy: control. Structural genes (regions that code for proteins) Regulatory gene produces repressor protein (not part of operon) Lactose is rarely presenting in the environment: this requires 3 proteins, ex: if there is no lactose, do you want the genes for the enzymes to be on , ans: no. If there is a low level or tryptophan, do you want the genes for the enzymes to be on : ans: yes. You want to make more tryptophan: ex: when no tryptophan is present, the repressor is ____ and the dna is _____ transcribed, active, is, active, is not, inactive, is, inactive, is not. Increase number of copies of a single gene and therefore increasing number of products produced.

Related Questions

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?

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

You are analyzing mutants in an Operon in an uncharacterized bacterial species using a method similar to what Jacob and Monod did to analyze the lac operon (see your text book Fig 14.7). This operon is induced in the presence of Sucrose to produce a sucrose metabolizing enzyme, the expression of which can be monitored using a reporter assay. A pink colored product is produced when an artificial substrate is added and the sucrose metabolizing enzyme is present. Like the ONPG assay, this assay is quantitative so the more enzyme, the darker the pink. In this operon, induction by sucrose is mediated by an Activator protein that when bound to its inducer sucrose, is able to bind to Operator A. The operon is also repressible by lactose. Repression by lactose is mediated by a Repressor protein that when bound to its co-repressor lactose, is able to bind to Operator B.

Based on this description, state whether the activator, the repressor, both, or neither would be bound to their respective operators under each set of conditions in wild type bacteria.

No Lactose

No Sucrose

Lactose

No Sucrose

No Lactose Sucrose

Lactose

Sucrose

Wild Type

A series of mutants is described below:

Activator Mutant A â Activator cannot bind to DNA

Activator Mutant B â Activator cannot bind to sucrose

Repressor Mutant A â Repressor cannot bind to DNA

Repressor Mutant B â Repressor cannot bind to lactose

Pink color was measured in wild type bacteria under the listed conditions. Based on the measurements in the wild type condition, state the amount of pink color that would be produced.

	-Lactose -Sucrose	+Lactose -Sucrose	-Lactose +Sucrose	+Lactose +Sucrose
Wild Type	0.030	0.030	1.891	0.124
Activator Mutant A
Activator Mutant B
Repressor Mutant A
Repressor Mutant B

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BIOL 1201 Lecture Notes - Lecture 15: Trp Operon, Operon, Repressor

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