Gene Regulation in Prokaryotes

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Questions and Answers

What is the main role of an inducer in gene regulation?

Triggers gene transcription by binding to a regulator protein (correct)

Inhibits the synthesis of certain enzymes

Acts as a constant repressor for gene expression

Prevents RNA polymerase from initiating transcription

Which type of genes are expressed at a fixed rate regardless of cell conditions?

Controllable genes

Constitutive genes (correct)

Inducible genes

Repressed genes

What leads to the repression of transcription in bacteria?

The action of RNA polymerase at the promoter

The binding of an inducer to the promoter

The binding of a repressor protein to DNA (correct)

The presence of substrates only

At what level is gene expression most efficiently controlled?

At the level of transcription Signup and view all the answers

What is a gratuitous inducer?

A molecule that induces enzyme synthesis but is not metabolized Signup and view all the answers

How long do E. coli messenger RNAs typically survive in vivo before degrading?

Close to 2 minutes Signup and view all the answers

What distinguishes controllable genes from constitutive genes?

Controllable genes respond to environmental conditions Signup and view all the answers

Which statement is true regarding co-repressors?

They are molecules that trigger repression of transcription Signup and view all the answers

What is the role of lac Y in the transport of P-galactosides?

It acts as a membrane bound protein for transporting P-galactosides into the cell. Signup and view all the answers

In which scenario does E. coli produce β-galactosidase?

When glucose is absent and lactose is present. Signup and view all the answers

What is the primary function of the repressor protein in the lac operon?

To interfere with the transcription of lactose metabolism genes. Signup and view all the answers

What is the structure of a functional repressor in the lac operon?

A homo tetramer formed from four identical copies of the repressor protein. Signup and view all the answers

What effect does the transferase have on β-galactosidase activity when glucose is present alongside lactose?

It prevents β-galactosidase from cleaving P-galactosides. Signup and view all the answers

What does the Lac operon represent in terms of gene regulation?

A common unit of transcription regulation Signup and view all the answers

Which of the following operates through negative inducible control?

Lac operon Signup and view all the answers

What type of gene products do trans acting sequences typically code for?

Regulator proteins Signup and view all the answers

In the context of operons, which sequence is an example of a cis acting site?

Promoter Signup and view all the answers

What is the role of the P-galactosidase enzyme coded by the lac Z gene?

To cleave lactose into glucose and galactose Signup and view all the answers

What do structural genes primarily code for?

Enzymes and proteins Signup and view all the answers

Which of the following defines a scenario where enzymes are produced only in the presence of a substrate?

Inducible system Signup and view all the answers

Which operon is characterized by negative repressible control?

Tryptophan operon Signup and view all the answers

What role does the lac repressor play in transcription regulation?

It prevents RNA polymerase from binding to the promoter. Signup and view all the answers

What is the consequence of the binding of the CAP-cAMP complex?

It enhances the transcription rate of the transcriptional unit. Signup and view all the answers

What happens to the cAMP levels in the presence of glucose?

cAMP levels decrease, inhibiting transcription. Signup and view all the answers

Which operator is located 410 bp downstream of lacZ?

O2 Signup and view all the answers

What is the role of an inducer in the context of the lac operon?

It helps in the release of the repressor. Signup and view all the answers

What structural change occurs in the DNA when the CAP-cAMP complex binds?

The DNA bends more than 90 degrees. Signup and view all the answers

What is catabolite repression primarily concerned with?

Prevention of alternative sugar usage. Signup and view all the answers

In which mechanism does the CAP-cAMP complex function?

Positive regulation. Signup and view all the answers

Study Notes

Gene Regulation In Prokaryotes

Induction: Occurs when bacteria synthesize certain enzymes only when their substrates are present. This results in switching on transcription due to the interaction of the inducer with the regulator protein.
Repression: Occurs when bacteria prevent synthesis of certain enzymes when their products are present. This involves inhibition of transcription by the binding of a repressor protein to a specific site on DNA (negative regulation).
Constitutive Genes: These are expressed at a fixed rate, regardless of cell conditions. Their genetic structure is simpler.
Controllable Genes: Their expression is only needed under specific conditions, and their amount may increase or decrease based on the condition. Their structure is comparatively complex with response elements.
Positive Regulation: Requires a transcription factor to bind at the promoter to enable RNA polymerase to initiate transcription.
Inducer: A small molecule that triggers gene transcription by binding to a regulator protein.
Gratuitous Inducers: Induce enzyme synthesis but are not metabolized.
Co-repressor: A small molecule that triggers repression of transcription by binding to a regulator protein.
Constitutive Gene Expression: The continuous expression of a gene that does not respond to any cellular conditions.
Gene Regulation: Can occur at the level of transcription, translation, or protein functioning. Transcriptional control is the most efficient.
E.coli Messenger RNA: Short-lived, degrading enzymatically within two minutes. This rapid turnover is necessary for transcriptional control.
Operon: Includes structural genes and control elements that regulate their expression.
Operon Model: A model that explains how genes are regulated in bacteria.
Negative Inducible Control: The Lac operon.
Negative Repressible Control: The Tryptophan operon.
Positive Inducible Control: The Arabinose operon.
Global Regulation/Multiple Controls: The Lac operon.
Post Translational Control: Regulates protein activity after it has been synthesized.
Cis-Acting Products: Sequences that code for products that act on genes physically connected to them.
Trans-Acting Products: The products of genes that can influence the transcription of other genes located elsewhere in the genome.
Promoter: The DNA region where RNA polymerase binds before starting transcription.
Terminator: The DNA sequence that signals the end of transcription.
Operator: The site on DNA where a repressor binds to prevent transcription initiation.
Catabolite Repression: Represses the Lac and Ara operons in the presence of glucose. This occurs due to the catabolism of glucose in preference to other sugars.
Cyclic AMP (cAMP): Works with the CAP protein to control the transcription of certain operons.
CAP (Catabolite Activator Protein): When combined with cAMP, enhances the affinity of RNA polymerase for the promoter.
CAP-cAMP Complex: Binds to a distal part of the promoter (CAP sites), enhancing the affinity of RNA polymerase for the promoter.
Lac Operon: A system in E. coli that controls the breakdown of lactose.
Glucose: Represses Lac operon.
Structural Genes: Codes for all RNA or protein products except for regulators.
Lac Z: Codes for β-galactosidase, which breaks down lactose into glucose and galactose.
Lac Y: Codes for lactose permease, a membrane-bound protein that transports lactose into the cell.
Lac A: Codes for thiogalactoside transacetylase, an enzyme that transfers an acetyl group from acetyl CoA to thiogalactosides.
Regulator Gene: Codes for a repressor protein.
Repressor Protein: Interferes with the transcription of genes involved in lactose metabolism.
Operator: The region where the repressor protein binds to prevent transcription.
Inducer: A molecule that binds to the repressor protein, causing it to detach from the operator.
Allolactose: An inducer of the Lac operon.
CAP Site: The site on the Lac operon where the CAP-cAMP complex binds.
Positive Regulation: Occurs when the transcription factor binds to the promoter region of its target gene, activating transcription and allowing for the expression of that gene.
Negative Regulation: Occurs when a repressor protein binds to the operator region, blocking the binding of RNA polymerase and preventing the transcription of its target gene.

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Description

Explore the mechanisms of gene regulation in prokaryotic organisms such as induction, repression, and the roles of constitutive and controllable genes. This quiz covers key concepts including positive regulation and the action of inducers on transcription. Test your knowledge on how these processes influence enzyme expression.