Transcriptional Regulation and Prokaryotic Gene Expression
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Questions and Answers

What primarily characterizes prokaryotic genes in terms of expression?

  • They require multiple initiators for transcription.
  • They are mostly constitutively expressed. (correct)
  • They do not utilize RNA polymerase.
  • They are regulated by complex mechanisms.

What is a polycistronic mRNA?

  • A transcript that cannot be translated.
  • A transcript encoding a single protein.
  • A transcript encoding multiple proteins. (correct)
  • A transcript with no leader sequence.

In prokaryotic gene regulation, what role do repressor proteins play?

  • They activate transcription directly.
  • They inhibit transcription. (correct)
  • They enhance RNA Polymerase binding.
  • They modify the promoter structure.

What is an operon?

<p>An expression unit consisting of related genes. (A)</p> Signup and view all the answers

What do the -10 and -35 elements in a promoter refer to?

<p>They are consensus sequences essential for RNA polymerase binding. (D)</p> Signup and view all the answers

What does negative regulation of transcription involve?

<p>Inhibition through repressor proteins. (B)</p> Signup and view all the answers

Which of the following describes a regulon?

<p>A group of operons regulated together. (D)</p> Signup and view all the answers

What is indicated by the term 'regulatory site' in the context of transcription?

<p>Regions where transcriptional activators or repressors bind. (D)</p> Signup and view all the answers

What is the primary function of an activator protein in transcription?

<p>It recruits RNA polymerase to the promoter. (A)</p> Signup and view all the answers

What role do architectural regulators serve in gene expression?

<p>They bend DNA to promote looping. (C)</p> Signup and view all the answers

How do transcription coactivators function in gene regulation?

<p>They bridge the RNA polymerase with activators. (A)</p> Signup and view all the answers

What is the function of insulators in gene expression?

<p>They block the unintended effects of DNA looping. (D)</p> Signup and view all the answers

What is a characteristic feature of the bacterial Lac repressor?

<p>It is composed of four identical subunits. (D)</p> Signup and view all the answers

In which way do transcription corepressors differ from activators?

<p>Corepressors suppress transcription by binding activators. (D)</p> Signup and view all the answers

What is the main role of DNA looping in transcriptional regulation?

<p>To enable recruitment of RNA polymerase by a promoter. (A)</p> Signup and view all the answers

What type of protein is CTCF, and what is its significance?

<p>A highly conserved zinc finger protein acting as an insulator. (A)</p> Signup and view all the answers

What is the primary role of an effector in gene transcription?

<p>It binds to activators or repressors, causing conformational changes. (D)</p> Signup and view all the answers

How can an effector inactivate a repressor?

<p>By causing the repressor to dissociate from DNA. (A)</p> Signup and view all the answers

Which of the following statements about effectors is incorrect?

<p>Effectors are typically large proteins. (B)</p> Signup and view all the answers

What happens when an effector is present and binds to an activator?

<p>The activator binds to DNA and stimulates transcription. (B)</p> Signup and view all the answers

Coordinated regulation of gene expression typically occurs in response to what?

<p>Stress responses. (B)</p> Signup and view all the answers

Which mechanism can lead to the global regulation of multiple genes?

<p>Removals of a common repressor by an effector. (D)</p> Signup and view all the answers

What effect does the absence of an effector have on activators?

<p>Activators bind DNA and facilitate transcription. (C)</p> Signup and view all the answers

What is NOT a way that effectors can regulate transcription?

<p>Binding directly to RNA. (B)</p> Signup and view all the answers

Flashcards

Operon

An expression unit consisting of one or more co-transcribed genes and the operator and promoter sequences regulating their transcription.

Regulon

A group of genes or operons that are coordinately regulated, even if spatially distant on the chromosome.

Negative regulation (transcription)

Repressor proteins inhibit transcription by binding to a regulatory site, preventing RNA polymerase from initiating.

Positive regulation (transcription)

Activator proteins enhance transcription by binding to a regulatory site, boosting RNA polymerase binding to the promoter.

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Repressor

A protein that binds to a regulatory site and inhibits transcription.

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Activator

A protein that binds to a regulatory site and increases transcription.

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Polycistronic mRNA

A single mRNA molecule that encodes multiple proteins.

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Operator

A specific DNA region where repressor proteins bind, influencing transcription initiation..

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Transcriptional activation by activators

Activator proteins bind near the gene's promoter region, recruiting RNA polymerase for transcription initiation.

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DNA looping (transcription)

Transcription activators binding distant regulatory sites on DNA can cause DNA to loop, bringing the activators closer to the promoter.

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Transcription coactivator

A protein that stimulates transcription by connecting RNA polymerase to activator proteins, without directly interacting with DNA.

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Transcriptional corepressor

A protein that can block gene expression by binding to activator proteins, preventing transcription.

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Insulators (gene expression)

Proteins that prevent unintended activation of genes by blocking DNA looping, keeping gene regulation specific.

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Transcriptional regulator (e.g., CTCF)

A protein that plays a role in organizing DNA structure to regulate gene transcription; often by bending DNA.

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DNA Looping

DNA can bend and connect distant segments facilitating protein-protein interactions. Promoters, activators, and RNA Pol are brought together by looping.

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Cis-regulatory elements

DNA sequences near a gene that affect its expression by interacting with regulatory proteins; can be located upstream, downstream, or within the gene.

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Effector

A small molecule that binds to a regulatory protein, like an activator or repressor, to influence gene expression.

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Effector's Role in Activator

An effector can bind to an activator, causing a conformational change that allows the activator to bind to DNA and promote transcription.

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Effector's Role in Repressor

An effector can bind to a repressor, causing a conformational change that releases the repressor from DNA, allowing transcription to occur.

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How does an effector inactivate an activator?

An effector can bind to an activator, changing its shape (conformation) and preventing it from binding to DNA, thus inhibiting transcription.

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How does an effector activate a repressor?

An effector binds to a repressor, changing its conformation to allow it to bind to DNA and shut down transcription.

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Global Gene Regulation

The coordinated control of the expression of multiple genes across the genome, often in response to stress.

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Global Regulation: Common Activator

Global regulation can occur by a single activator protein that controls the expression of multiple genes.

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Global Regulation: Common Repressor

Global regulation can occur by a single repressor protein that controls the expression of multiple genes.

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Study Notes

Transcriptional Regulation of Gene Expression

  • Regulatory DNA-binding proteins control gene expression
  • Text sections covered: 19.1-19.2, 20.1 (SOS response)
  • Key terms: activation, repression, activator, repressor, regulatory site, positive regulation, negative regulation, DNA looping, coactivator, corepressor, insulator, effector, polycistronic mRNA, operon, regulon

Prokaryotic Gene Expression

  • Prokaryotic DNA is less condensed than eukaryotic DNA
  • Prokaryotic genes are often constitutively expressed
  • RNA polymerase generally has access to all promoters
  • Promoters have -10 and -35 elements
    • -10 element (TATA box/Pribnow box) consensus sequence: TATAAT/A
    • -35 element consensus sequence: TTGACA
  • Regulatory molecules affect RNA polymerase binding to the promoter
    • Operator: repressor binding site
    • Activator binding site:Activator binding site
  • Genes transcribed as a unit

Polycistronic mRNA

  • A transcript encoding multiple proteins
  • Includes a leader sequence preceding the first gene
  • Subsequent genes are followed by intercistronic regions

Operon

  • An expression unit consisting of one or more co-transcribed genes and their regulatory sequences

Regulon

  • A group of genes or operons that are coordinately regulated
  • Genes may be spread throughout/distant in the chromosome/genome

Negative Regulation

  • Repressor proteins inhibit transcription
  • Repressor-binding site overlaps the promoter
  • Repressor binding prevents RNA polymerase from initiating transcription

Positive Regulation

  • Some genes need activators to bind to their promoters to initiate transcription
  • Activators recruit RNA polymerase to the promoter
  • Transcription then initiates

Transcriptional Regulation From a Distance: DNA Looping

  • Some transcription activators bind to a distant regulatory site
  • Enabling the promoter and RNA polymerase complex to form a DNA loop

DNA Looping Mediation

  • Single regulatory proteins (e.g., Lac repressor) bind to two distant sites
  • Forming a DNA loop

Architectural Role of Regulatory Proteins

  • Architectural regulators bend DNA
  • Promoting DNA looping

Transcription Coactivator

  • A protein that facilitates transcription
  • "Bridges" RNA polymerase with transcription activators
  • Does not directly bind DNA. (e.g., Mediator complex)

Transcription Corepressor

  • A protein that binds to an activator to suppress transcription
  • Does not bind RNA polymerase
  • (e.g., Yeast Cys8)

Insulators

  • Block unintended effects of distant DNA looping
  • Present in both prokaryotes and eukaryotes
  • Prevents cross-talk between regulators of different promoters
    • CTCF (CCCTC-binding factor) is an example of a highly conserved zinc finger protein, acting as an insulator

Effectors

  • Small molecules (not proteins)
  • Bind to activators or repressors
  • Induce a conformational change
  • Results in increased/decreased transcription of a target gene

SOS Response (global regulation)

  • Mechanism for repairing damaged DNA in bacteria
  • Expression of multiple genes involved in repair is coordinated
  • Requires two key proteins: RecA and LexA
    • LexA normally represses SOS genes
    • RecA protein (activated if DNA is damaged) triggers LexA autocleavage, removing repression, allowing transcription of SOS genes

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BIOL 366 Lecture 11 on Transcriptional Regulation PDF

Description

Explore the intricacies of transcriptional regulation and prokaryotic gene expression in this quiz. Understand the roles of regulatory proteins, DNA elements, and polycistronic mRNA. Key concepts include activation, repression, and the importance of promoter elements in prokaryotes.

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