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Questions and Answers
Which component of the operon acts as an on/off switch for transcription?
Which component of the operon acts as an on/off switch for transcription?
What is the function of the corepressor in gene regulation?
What is the function of the corepressor in gene regulation?
In negative regulation of gene expression, what is the role of the repressor protein?
In negative regulation of gene expression, what is the role of the repressor protein?
What is the key role of an inducer in gene regulation?
What is the key role of an inducer in gene regulation?
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In positive regulation of gene expression, what is required for RNA polymerase to initiate transcription?
In positive regulation of gene expression, what is required for RNA polymerase to initiate transcription?
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Where does the repressor protein bind in the lac operon when lactose is absent?
Where does the repressor protein bind in the lac operon when lactose is absent?
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What is the function of LacA in the lac operon?
What is the function of LacA in the lac operon?
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Which element directly influences target gene transcription by binding to cis-acting elements?
Which element directly influences target gene transcription by binding to cis-acting elements?
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What is the role of insulators in gene regulation?
What is the role of insulators in gene regulation?
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In Eukaryotes, what is the function of transcriptional activators like Sp1?
In Eukaryotes, what is the function of transcriptional activators like Sp1?
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Where are cis-acting elements located and what do they directly regulate?
Where are cis-acting elements located and what do they directly regulate?
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What is the function of enhancers in eukaryotic gene regulation?
What is the function of enhancers in eukaryotic gene regulation?
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What initiates the transcription of the lac operon by rendering the repressor protein inactive?
What initiates the transcription of the lac operon by rendering the repressor protein inactive?
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Study Notes
Operon
- A group of genes that are transcribed together and code for functionally similar proteins
- Consists of promoter, operator, and genes for proteins
Key Players in Operon
- Promoter: a section of DNA where RNA polymerase binds
- Operator: controls activation of transcription, acting as an on/off switch between the promoter and genes for proteins
- Repressor protein: binds to the operator to block RNA polymerase and shut down transcription
- Corepressor: keeps the repressor protein on the operator
- Inducer: pulls the repressor off the operator, turning on the operon
Types of Gene Regulation
- Negative Regulation: a repressor protein binds to an operator to prevent a gene from being expressed
- Positive Regulation: a transcription factor is required to bind at the promoter to enable RNA polymerase to initiate transcription
Lac Operon Components
- Structural Genes:
- LacZ: encodes β-galactosidase, an enzyme that cleaves lactose into glucose and galactose
- LacY: codes for lactose permease, enabling lactose entry into the cell
- LacA: encodes transacetylase, which modifies lactose metabolites for excretion
- Operator (O): regulatory DNA sequence where a repressor protein binds, inhibiting transcription when lactose is absent
- Regulatory Genes:
- LacI: encodes the repressor protein, which suppresses transcription in the absence of lactose
- Inducer Molecule (Lactose): initiates operon transcription by binding to the repressor protein, rendering it inactive
The Central Principle of Gene Regulation
Cis-Acting Elements
- Definition: DNA sequences on the same chromosome as the regulated gene
- Function: Directly regulate adjacent genes, e.g., promoters, enhancers, silencers, operators
- Location: Non-coding regions: upstream (promoter), downstream (terminator), or within introns
- Effect: Modulate transcription rate, impacting overall gene expression levels
Trans-Acting Factors
- Definition: Proteins or molecules regulating genes, produced by different genes, binding to cis-acting elements
- Function: Bind to cis-acting elements, directly influencing target gene transcription
- Location: Synthesized in the same or different cells within an organism
- Effect: Presence, absence, and affinity for cis-acting elements dictate gene expression levels
Regulation of Transcription in Eukaryotes
- Eukaryotic DNA: packaged into chromatin, which limits its availability as a template for transcription
- Non-coding RNAs and Proteins: regulate transcription via modifications of chromatin structure
- Cis-Acting Sequences: many regulate expression of eukaryotic genes
- Identification of Eukaryotic Regulatory Sequences: using Gene Transfer Assays and Transfection
Promoter
- Definition: The region of DNA involved in the initiation of transcription
- Function: Provides a binding site for RNA polymerase and other proteins necessary for transcription
Enhancers
- Definition: Regulatory sequences located farther away from the start site
- Function: Bind transcription factors that then regulate RNA polymerase
- Location: Can be located at a distance from the promoter, and can even be found on a different chromosome
Repressors
- Definition: Proteins that inhibit gene expression by binding to specific DNA sequences
- Function: Turn off transcription by blocking activators from binding to enhancers
Insulators
- Definition: Specific DNA sequences that define chromatin domain boundaries
- Function: Regulate interactions between enhancers, silencers, and promoters
- Role: Maintain enhancer-promoter specificity, and organize chromosomes into looped domains
Transcriptional Activators
- Definition: Proteins that stimulate transcription by binding to regulatory DNA sequences
- Have two independent domains: one region binds DNA, the other stimulates transcription
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Description
Test your knowledge on the transcriptional regulation and epigenetics in prokaryotes, focusing on the operon concept. Learn about key players like promoter, operator, repressor protein, and corepressor.
