BIOB11H3 Lecture 10: BIOB11 – Lecture 10

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apricotbat126

13 Feb 2017

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Operon: cluster of genes that are typically coordinately regulated. Regulatory gene: encode proteins which bind to operator sequences and influence the transcription competency of the operon. Repressor: dna or rna binding protein that inhibits the expression of one or more genes by binding to the operator or associated silencers. Inducer: a molecule that regulates gene expression; binds to repressors or activators; function by disabling respressors. Co-repressor: substance that inhibits the expression of genes; does not directly bind to dna but instead indirectly regulates gene expression by binding to repressors. Derepression: removal of repression such as of an operon so that gene transcription occurs or is enhanced, with the net result frequently being elevation of the level of a specific enzyme. Positive vs. negative control: negative control: an active repressor blocks gene expression by binding to an operator site, positive control: an active factor is required for gene expression.

Related Questions

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

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?

3. Assume that in a bacterial species you discover a cluster ofthree genes (A, B, and C) that accountfor the enzymatic production of a cellulose-like carbohydrate (clc)that is needed as a component of its cell wall. When there issufficient clc is in the cell, the three enzymes are notsynthesized. However, when more clc is needed, the three enzymesare abundantly produced. This cluster of genes appears to be undercoordinate control because deletion of a distant gene (R)results in constitutive expression of all three genes even whenexcess clc is present. When mutations (P^-) occur in a region upstream ofgene A, no synthesis of the three enzymes occurs even whenclc levels are extremely low. Mutations (O ^-)that occur right next to the P ^- mutationsresult in constitutive expression of all three genes even when clcis present at high levels.

(a) Do the three genes (A, B,and C) behave as if they were part of an operon?

(b) What type of control (positive or negative)seems likely to control the production of the three enzymes?

(c) What is the most likely function of theprotein produced from gene R?

(d) Do you expect that clc is an inducer,inhibitor, or corepressor?

(e) You discover that clc binds to the proteinmade from gene R. What is the most likely effect of this binding?(Hint: will it cause the R protein to bind DNA or fall off ofthe DNA?)

(f) Where do you think protein R binds?(Hint: P region or O region ?)

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BIOB11H3 Lecture 10: BIOB11 – Lecture 10

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