BIOL2161 Lecture 8: BIOL2161 - Gene structure, expression & regulation in prokaryotes

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maroonbear853

14 Jun 2018

School

ANU

Department

Biology

Course

BIOL2161

Professor

Professor Susan Howitt

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BIOL6: Genes: Replication and Expression

Block 2: Gene structure & regulation in prokaryotes

Operon Case Studies

• Lactose (allolactose): prevents repressor from binding to operator

• cAMP: causes the activator to bind to the operator regions

• Components necessary to regulate lac operon:

o DNA: containing promoter and operator

o Activator: binding cAMP - glucose sensor

o Repressor: binding lactose - lactose sensor

o RNA polymerase

• How does lactose get into the cell? Where does allolactose come from?

o Produced by beta-galactosidase

o Answer: low intrinsic (background) transcription. It is just much, much more when

lactose is around (upregulation)

o Upon addition of lactose, there is a positive feedback loop

• Negative control

o Inducible (normally off): substrate inactivates repressor

• Lac operon

o Repressible (normally on): product activates repressor

• Tryptophan (trp) operon

▪

• Positive control

o Inducible (normally off): substrate activates activator

o Repressible (normally on): product activates activator

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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.

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BIOL2161 Lecture 8: BIOL2161 - Gene structure, expression & regulation in prokaryotes

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