Gene Expression and Regulation

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Questions and Answers

Which type of operon is normally in an 'on' state and is inhibited by the presence of tryptophan?

Repressible Operon (correct)

Inducible Operon

Constitutive Operon

Polygenic Operon

What is the role of the CAP-cAMP complex in the lac operon under low glucose conditions?

Enhances transcription (correct)

Promotes corepressor activity

Inhibits RNA polymerase activity

Decreases repressor binding

Which element is considered a cis-acting element that can increase transcription by interacting with activators?

Promoter

Core promoter

Enhancer (correct)

Silencer

What function do RNA binding proteins serve in translational regulation?

Bind to the 5' UTR of mRNA Signup and view all the answers

Which modification to histones generally leads to increased transcription by loosening the chromatin structure?

Histone Acetylation Signup and view all the answers

Which of the following accurately describes transcriptional regulation by the mediator complex?

It coordinates interactions between regulatory proteins and RNA polymerase. Signup and view all the answers

In the trp operon, what occurs in the absence of tryptophan?

Transcription is active. Signup and view all the answers

Which of the following statements about alternative splicing is correct?

It allows for multiple protein isoforms from a single gene. Signup and view all the answers

Which factor primarily regulates the binding of repressors in the operon model?

Corepressors Signup and view all the answers

What effect does DNA methylation generally have on transcription?

It blocks transcription by compacting chromatin. Signup and view all the answers

What is the role of inducers in the context of regulated gene expression?

They promote transcription by disabling repressors. Signup and view all the answers

What does the presence of core promoters indicate in transcription regulation?

They are essential for transcription initiation. Signup and view all the answers

Which of the following best describes the function of small interfering RNA (siRNA) in gene expression?

It degrades mRNA via perfect complementarity. Signup and view all the answers

What is the primary role of enhancers in gene regulation?

Increase transcription by interacting with activators Signup and view all the answers

What type of RNA molecule is involved in degrading mRNA through perfect complementarity?

Small Interfering RNA (siRNA) Signup and view all the answers

Which gene is known for regulating cell signaling and is commonly mutated in cancer?

Ras Signup and view all the answers

How does phosphorylation affect the Retinoblastoma (Rb) protein?

Inhibits its ability to bind E2F, allowing cell cycle progression Signup and view all the answers

What is the '2-Hit' model of cancer development?

One hit is inherited and the second hit is somatic for sporadic cancers Signup and view all the answers

What is the primary function of tumor-suppressor genes?

Regulate the cell cycle or repair DNA Signup and view all the answers

Which of the following describes the effect of glucocorticoid hormones on gene activation?

They activate genes through hormone response elements (GREs) Signup and view all the answers

What is the mechanism of action for RNA binding proteins in translational regulation?

They bind to the 5′ UTR of mRNA to regulate efficiency or stability Signup and view all the answers

What is one characteristic that differentiates oncogenes from proto-oncogenes?

Oncogenes require only one allele to be mutated for overactivity Signup and view all the answers

What defines the role of metallothionein IIA gene (hMTIIA)?

Encodes a protein that binds heavy metals for protection Signup and view all the answers

Study Notes

Gene Expression

Constitutive: Genes expressed constantly, encoding essential proteins.
Regulated: Genes expressed in response to environmental changes.
Operons: Sets of genes transcribed together, producing polycistronic mRNA for multiple proteins.
- Promoter: RNA polymerase binding site.
- Operator: Repressor protein binding site.
- Inducible Operons: Usually off, activated by inducers (like lactose)
- Repressible Operons: Usually on, inhibited by corepressors (like tryptophan).

Regulatory Genes

Encode proteins that control gene expression. (Trans-acting)
Repressors: Bind the operator to block transcription.
- Inducers: Promote transcription by disabling repressors.
- Corepressors: Inhibit transcription by enabling repressors..
Activators: Enhance transcription by promoting RNA polymerase binding.
- Inhibitors: Inhibit transcription by disabling activators.

Lac Operon (Inducible)

No Lactose: Repressor blocks transcription.
Lactose Present: Allolactose (inducer) binds repressor, allowing transcription.
- Cis-acting elements: Physically attached to the gene (e.g., lacO - operator, lacP - promoter).
- Trans-acting genes: Control genes located elsewhere (e.g., lacI - encodes repressor).
- Structural genes: Encode proteins involved in lactose metabolism (e.g., lacZ encodes β-galactosidase, lacY encodes permease, lacA encodes transacetylase).
- CAP-cAMP: Low glucose stimulates cAMP (high levels), enhancing transcription. High glucose reduces cAMP, reducing transcription.

Trp Operon (Repressible)

No Tryptophan: Transcription active, synthesizing enzymes.
Tryptophan Present: Tryptophan acts as a corepressor, enabling the repressor, blocking transcription.

Chromatin Remodeling

Histone Acetylation: Loosens chromatin, allowing transcription.
DNA Methylation: Inhibits activator binding, compacts chromatin, decreases transcription, often at CpG islands.
Histone Methylation: Activators bind enhancers, increasing transcription; repressors bind silencers, decreasing transcription.
Mediator Complex: Coordinates regulatory proteins and RNA polymerase; regulates transcription initiation/elongation.

Promoters

DNA sequences where transcription begins.
Core Promoter: Contains the TATA box (critical for binding).
Proximal Promoter: Closer to the start site, contains CCAAT box, GC boxes (enhance transcription).
Distal Promoter: Farther from the start site, includes enhancers and silencers.

Cis-Acting Elements

DNA sequences regulating nearby genes.
Enhancers: Increase transcription.
Silencers: Decrease transcription.

Trans-Acting Elements (Proteins)

Proteins interacting with cis-elements to regulate transcription.
Zinc Finger, Helix-Turn-Helix, Leucine Zipper, Helix-Loop-Helix: Different protein motifs for binding specific DNA sequences.

Post-Transcriptional Regulation

Alternative Splicing: Different protein products from a single gene.
RNA Editing: Changing mRNA sequence after transcription.
RNA Interference (RNAi): Small RNA molecules degrade mRNA, or block translation.
- MicroRNAs (miRNAs): Endogenous; partial complementarity inhibits translation.
- Small Interfering RNA (siRNA): Exogenous; perfect complementarity degrades mRNA.

Translational Regulation

RNA Binding Proteins: Regulate translation efficiency/stability by binding mRNA 5' UTR.

Applications (Examples)

Glucocorticoid Hormones: Regulate genes via hormone response elements.
GloFish: Fluorescent genes (GFP/RFP) with constitutive promoters for monitoring/decoration.
Metallothionein IIA: Protein for heavy metal binding, responsive to heavy metal response elements (MREs).

Cancer Development

Definition: Uncontrolled cell growth.
Causes: Oncogene activation, tumor suppressor inactivation.
Characteristics: Altered shape, lack of contact inhibition, metastasis.
Cell Cycle Regulation: Controlled by cyclins and CDKs.
- Knudson's "Two-Hit" Model: Cancer requires multiple mutations (both alleles of a tumor suppressor must be inactivated).
Proto-Oncogenes and Oncogenes: Proto-oncogenes promote normal cell division, oncogenes cause uncontrolled growth; Ras gene is an example.
- Dominant mutations; only one allele needs to be mutated.
Tumor Suppressor Genes: Regulate cell cycle and/or repair; loss leads to uncontrolled growth.
- Examples include Rb gene (prevents cell cycle progression), and p53 gene (halts cell cycle or apoptosis).

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Description

Explore the intricacies of gene expression, focusing on constitutive and regulated genes, as well as operons. This quiz covers pivotal concepts like promoters, operators, and the regulation mechanisms involving repressors and activators, including detailed discussions on the Lac operon. Test your knowledge of these essential genetic processes.