Molecular Biology: Gene Regulation Mechanisms

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Questions and Answers

What is the role of the repressor protein in the synthesis of tryptophan?

It remains inactive when tryptophan levels are low. (correct)

It decreases tryptophan levels by blocking structural genes.

It activates tryptophan production when levels are high.

It enhances the expression of the tryptophan operon.

How do transcriptional activators influence gene expression?

They bind to DNA and inhibit transcription.

They modify chromatin structure to block transcription.

They solely bind at the transcription start site.

They interact with the Mediator and enhance transcription initiation. (correct)

What occurs when tryptophan levels are high?

Tryptophan synthase is produced at a higher rate.

The operon is activated and tryptophan is synthesized.

The repressor binds to tryptophan, inhibiting operon expression. (correct)

The structural genes are permanently turned on.

Which mechanism do transcriptional factors utilize to exert control over gene expression?

Interacting with co-activators and chromatin remodeling complexes. Signup and view all the answers

What is the primary function of transcriptional repressors?

To silence gene expression by inhibiting transcription. Signup and view all the answers

Which factor is NOT a characteristic of transcription factors?

They can operate independently of each other. Signup and view all the answers

What happens to chromatin structure during transcriptional activation?

It undergoes remodeling to become more relaxed. Signup and view all the answers

In what way do multiple transcription factors collaborate?

By binding at distant regulatory regions to control expression. Signup and view all the answers

What is one primary role of miRNA in cellular processes?

Inhibiting translation of specific mRNAs Signup and view all the answers

What is a function of eIF4E-binding proteins (4E-BPs) when growth factors are absent?

Blocking translation initiation Signup and view all the answers

How do repressor proteins influence translation initiation?

By interfering with eIF4A Signup and view all the answers

What does the phosphorylation of eIF2 accomplish in translation regulation?

It inhibits translation by preventing initiation Signup and view all the answers

What is a consequence of miRNA interaction with the 3’ UTR of target mRNA?

Inhibition of mRNA translation Signup and view all the answers

What mechanism do microRNAs use to influence global translational activity?

By degrading specific mRNAs Signup and view all the answers

Which of the following is NOT a process influenced by miRNAs?

Transcription elongation Signup and view all the answers

What ultimately occurs after the phosphorylation of eIF4E-binding proteins (4E-BPs)?

Dissociation from eIF4E Signup and view all the answers

What is the primary initial step in mRNA degradation?

Deadenylation of the poly-A tail Signup and view all the answers

Which of the following factors can influence the rate of mRNA degradation in eukaryotes?

The presence of AU-rich sequences near 3' ends Signup and view all the answers

How do RNA-binding proteins (RBPs) modify the fate of mRNA?

By binding to regulatory sequences Signup and view all the answers

What role do microRNAs (miRNAs) play in mRNA degradation?

They cause deadenylation of the mRNA. Signup and view all the answers

What is a significant characteristic of mRNAs in prokaryotes compared to eukaryotes?

They have short half-lives lasting only minutes. Signup and view all the answers

What type of chromatin is typically transcriptionally active?

Euchromatin Signup and view all the answers

What is required for translation initiation in eukaryotes?

mRNA, amino-acyl tRNA (met), ribosome, and protein initiation factors Signup and view all the answers

Which histone modification is primarily associated with increased transcriptional activity?

Acetylation Signup and view all the answers

What happens to ferritin translation when iron levels are low?

Translation halts due to IRP binding Signup and view all the answers

What role do histone deacetylases (HDACs) play in chromatin regulation?

They remove acetyl groups from histones. Signup and view all the answers

What is a common target for DNA methylation?

Cytosines in CpG dinucleotides Signup and view all the answers

Which of the following agents is involved in the regulation of translation initiation?

Repressor proteins Signup and view all the answers

What structure forms during the micro RNA (miRNA) duplex formation?

Double stranded hairpin structure Signup and view all the answers

Which histone modification can lead to transcriptional repression?

Methylation of histones Signup and view all the answers

What is the function of DNA methyltransferases?

To introduce methyl groups into DNA Signup and view all the answers

What does the repressor protein binding to the 5' untranslated regions of mRNA affect?

It interferes with translation initiation Signup and view all the answers

How does global translational activity get affected?

By various agents including micro RNAs and specific mRNAs Signup and view all the answers

How does acetylation of lysine 16 on histone H4 affect chromatin structure?

It keeps chromatin in a highly opened state. Signup and view all the answers

What is the role of Drosha and Dicer in miRNA processing?

They generate double stranded miRNA Signup and view all the answers

What is the consequence of promoter methylation in DNA?

Transcriptional silencing Signup and view all the answers

Which component is NOT directly involved in the initiation of translation?

Repressor proteins Signup and view all the answers

What is the role of repressor proteins in translation regulation?

They block the initiation of translation by binding to specific regions of mRNA. Signup and view all the answers

What is one mechanism through which miRNAs regulate mRNA?

By binding to the 3’ UTR of specific mRNAs to inhibit translation. Signup and view all the answers

How is RNA degradation enhanced by miRNA?

By interacting with the 3’ UTR of mRNA via RISC. Signup and view all the answers

In eukaryotes, what primarily controls gene expression?

Transcription factors and chromatin modifying enzymes. Signup and view all the answers

What is the function of 5' exonucleases in RNA degradation?

They remove the 5’ MeG cap from RNA. Signup and view all the answers

What describes the genetic control mechanism in prokaryotes?

They utilize operons that can be either inducible or repressible. Signup and view all the answers

Which process can contribute to the diversity of gene expression in eukaryotes?

Alternative splicing. Signup and view all the answers

How do growth factors influence global translation regulation?

Through kinase activation and inhibition of translation initiation. Signup and view all the answers

Study Notes

Genetic Control Mechanisms 1: Controlling Gene Expression

Gene expression is controlled at multiple steps, starting within the nucleus and continuing into the cytosol.
Steps include: transcriptional control, RNA processing control, alternative splicing, RNA transport and localization control, translation control, and protein activity control.
During transcriptional control, the expression of a gene is regulated.
RNA processing control involves how the RNA transcript is processed prior to translation.
Alternative splicing allows a single gene to produce multiple proteins.
RNA transport and localization control regulates mRNA movement and location within the cell.
Translation control regulates the translation of mRNA into protein.
Protein activity control regulates the activity of the protein product.

Bacterial Operons

Operons are functioning units of genomic DNA containing a cluster of genes under the control of a single promoter.
The operon's components include a promoter, an operator, and structural genes that code for enzymes.
The lac operon is a system in E. coli that regulates the efficient use of lactose as a substrate.
The synthesis of enzymes is induced by the presence of lactose.
The lac operon consists of genes encoding beta-galactosidase, lactose permease, and transacetylase.

Lac Operon Repression

The i gene encodes a repressor protein that binds to the operator site on the lac operon.
The binding of the repressor protein blocks the transcription of the z, y, and a genes.
Allolactose, derived from lactose, binds to the repressor protein and inactivates it.
Transcription of z, y, and a genes proceeds, allowing the expression of enzymes necessary for lactose metabolism.

Repressible Systems (e.g., trp operon)

The trp operon codes for genes responsible for tryptophan synthesis.
When tryptophan levels are high, the repressor protein is activated and binds to the operon, preventing expression of genes for tryptophan synthesis.
When tryptophan levels are low, the repressor protein is inactive, and the operon is activated.

Transcriptional control in eukaryotes

In eukaryotes, transcription is chiefly controlled by regulatory transcription factors.
Transcription factors can activate or repress transcription and can operate via interactions with the mediator and general transcription factors involved in transcriptional initiation.
The action can happen via modifying chromatin structure.

Chromatin Remodeling and Activity

Euchromatin represents a loosely packed chromatin structure linked to transcriptional activity.
Heterochromatin represents a densely packed chromatin structure linked to less transcriptional activity.
Modifications of histones like acetylation alter chromatin structure.
Modification of histones via specific enzymes like histone acetyltransferases and histone deacetylases impact transcriptional activity.

mRNA Degradation

mRNA degradation is usually initiated by deadenylation of the poly-A tail.
This leads to 3' to 5' exonuclease digestion.
Removal of the 5' methylguanosine cap can also initiate degradation through 5' to 3' exonuclease digestion.
mRNA degradation is a regulatory mechanism where different mRNA types can be degraded at different rates, influencing gene expression.

Translation Regulation

Translation initiation in eukaryotes includes mRNA, amino-acyl tRNA (Met), ribosome, GTP and 12 initiation factors. Initiation involves translocation of a complex along mRNA to AUG (Start) sites.
Translation initiation within eukaryotes is regulated by repressor proteins (protein kinases + elF binding proteins), microRNAs, and specific mRNAs, influencing global translational activity.
Phosphorylation of elF2 and elF2b impacts translation. Growth factors stimulate the phosphorylation, while growth factor deprivation blocks the process.
4E-BPs regulate eIF4E, affecting translation initiation.

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Description

Explore the intricate roles of transcriptional factors, repressors, and miRNAs in gene expression regulation. This quiz examines key mechanisms involved in the synthesis of tryptophan and the resultant effects on cellular processes. Test your understanding of how these molecules interact and influence transcription and translation.