Gene Regulation and Expression Quiz

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Questions and Answers

Which of the following is NOT a characteristic of regulated genes?

They are expressed only under certain conditions.

They may be expressed in all cells or only in a subset of cells.

Their expression is continually expressed. (correct)

Their regulated expression is the basis for cellular differentiation, morphogenesis and adaptability of organisms.

What is the primary function of a promoter sequence?

To bind to specific transcription factors (repressors) and inhibit transcription.

To bind to RNA polymerase and initiate translation.

To serve as binding sites for basal transcription protein factors and RNA polymerase. (correct)

To bind to specific transcription factors (activators) and stimulate transcription.

Enhancer sequences are characterized by:

Always being close to the promoter sequence.

Binding to specific transcription factors (activators) and increasing transcription. (correct)

Binding only to RNA polymerase for transcription initiation.

Being located only upstream of the +1 position.

What is the main difference between cis-acting and trans-acting elements in gene regulation?

Cis-acting elements are located on the same chromosome as the gene they regulate, while trans-acting elements are encoded by different genes. Signup and view all the answers

What does the term 'constitutive' mean in the context of gene expression?

Genes that are expressed in all cells at a constant level. Signup and view all the answers

Which of the following is an example of a 'regulated' gene?

A gene encoding a protein responsible for producing a specific hormone in response to a signal. Signup and view all the answers

What is the significance of regulated gene expression?

It allows for adaptation to changing environmental conditions and cellular differentiation. Signup and view all the answers

How do 'silencer' sequences differ from 'enhancer' sequences?

Silencer sequences bind to specific transcription factors (repressors) and decrease transcription, while enhancers bind to specific transcription factors (activators) and increase transcription. Signup and view all the answers

What is the role of cAMP in the regulation of gene expression by glucagon?

cAMP activates protein kinase A, which phosphorylates CREB, leading to the activation of genes with CRE in their promoters. Signup and view all the answers

How do steroid hormones regulate gene expression?

Steroid hormones enter the cell and bind to intracellular receptors, forming complexes that activate gene expression. Signup and view all the answers

What is the role of iron regulatory proteins (IRPs) in the regulation of transferrin receptor mRNA stability?

IRPs bind to IRES in transferrin receptor mRNA when iron levels are low, stabilizing the mRNA and increasing transferrin receptor synthesis. Signup and view all the answers

Which of the following is NOT a mechanism of regulation of gene expression at the DNA level in eukaryotes?

RNA splicing and processing. Signup and view all the answers

Give an example of how DNA rearrangements can regulate gene expression.

The production of immunoglobulins by B-lymphocytes through gene rearrangement. Signup and view all the answers

What is the result of the editing of apo B mRNA in intestinal cells?

The creation of a stop codon at codon 2153 Signup and view all the answers

Which of the following accurately describes the proteins produced from apo B mRNA?

Apo B-48 represents only 48% of the apo B-100 protein length. Signup and view all the answers

What type of gene regulation is involved in the differential expression of apo B mRNA in hepatocytes versus intestinal cells?

Posttranscriptional editing Signup and view all the answers

In what way do hepatocytes and intestinal cells differ in processing apo B mRNA?

Intestinal cells perform specific mRNA editing that hepatocytes do not. Signup and view all the answers

What type of modification occurs to the apo B mRNA that alters its final protein product in intestinal cells?

Deamination of cytosine into uracil Signup and view all the answers

What do general (basal) transcription factors specifically recruit during the initiation of transcription?

RNA polymerase Signup and view all the answers

Which type of transcription factors interact with enhancer and silencer DNA sequences?

Specific transcription factors Signup and view all the answers

What is the function of coactivators in gene transcription?

Interact with specific transcription factors Signup and view all the answers

Which epigenetic mechanism is associated with altering DNA structure to make it accessible for transcription?

Chromatin remodeling Signup and view all the answers

How do specific transcription factors modulate the efficiency of transcription initiation?

By interacting with general transcription factors and RNA polymerase Signup and view all the answers

What is the effect of DNA bending during transcription regulation?

Allows interaction between distal regulatory elements and the promoter Signup and view all the answers

Which type of transcription factor is not capable of binding to DNA?

Coactivators Signup and view all the answers

What role does histone acetyltransferase (HAT) play in gene regulation?

It facilitates chromatin remodeling by acetylation Signup and view all the answers

What is the process called when chromatin transitions between active and inactive forms?

Chromatin Remodeling Signup and view all the answers

What is the primary difference between euchromatin and heterochromatin?

Euchromatin is associated with active transcription, while heterochromatin is associated with inactive transcription. Signup and view all the answers

What is the effect of histone acetylation on chromatin structure?

It decreases the positive charge of histones, leading to looser DNA wrapping. Signup and view all the answers

How does DNA methylation directly interfere with transcription?

By preventing the binding of transcriptional factors to the promoter region. Signup and view all the answers

Which of the following is TRUE about the relationship between DNA methylation and histone acetylation?

DNA methylation and histone acetylation often work together to repress gene expression. Signup and view all the answers

What is the role of CpG dinucleotides in DNA methylation?

CpG dinucleotides are the primary sites of methylation in vertebrate DNA. Signup and view all the answers

Which of these is TRUE regarding active chromatin?

It is predominantly unmethylated and has high levels of acetylated histone tails. Signup and view all the answers

What is the direct outcome of chromatin remodeling in the context of gene expression?

It controls the accessibility of DNA for transcription. Signup and view all the answers

Study Notes

Course Information

Course: BMS 141
Lecture Number: 12
Title: Regulation of Gene Expression
Instructor: Dr. Lamees Dawood
Program: Medicine and Surgery
Semester: Fall 2024
University: Galala University, powered by Arizona State University

Gene Regulation: Different Control Sites

Regulation occurs at various levels: Transcription, posttranscriptional processes of mRNA, posttranslational processes, and DNA-related mechanisms in eukaryotes.

Constitutive vs. Regulated Genes

Constitutive (Housekeeping) Genes: These genes continuously produce proteins needed for basic cellular functions. They are not regulated.
Regulated Genes: These genes are only expressed under specific conditions, such as in certain cells, at a given time, or in response to specific signals (e.g., hormones). This regulated expression is crucial for cellular differentiation, morphogenesis, and adaptability in organisms.

I- At the Level of Transcription

Transcription synthesizes RNA.
This process is DNA-directed and RNA synthesis is carried out by RNA polymerase.

Glossary: Cis-Acting DNA Sequences

Promoter Sequences: Located upstream of the transcription start site (+1 position), acting as binding sites for basal transcription factors and RNA polymerase.
Enhancer Sequences: Can be located upstream or downstream or thousands of base pairs away from the transcription start site, acting as binding sites for specific transcription factors (activators).
Silencer Sequences: Similar to enhancer sequences but bind to specific transcription factors to repress gene expression (repressors).

Glossary: Trans-Acting Transcription Factors (Protein Factors)

General (Basal) Transcription Factors: Protein factors that recognize and bind to promoter sequences, initiating transcription by recruiting RNA polymerase.
Specific Transcription Factors: Protein factors that bind to DNA sequences. Activators bind to enhancers and repressors bind to silencers. These factors can regulate transcription in response to signals (e.g., hormones).

1. General or Basal TFs

Bind to consensus sequences of the promoter.
Important in assembly of the initiation complex and recruitment of RNA polymerase II.
Catalyze basal or constitutive transcription.

2. Specific or Regulatory TFs

Bind to regulatory sequences (enhancers or silencers).
Modulate transcription initiation efficiency.
Mediate responses to signals (e.g., hormones).
Regulate gene expression at specific times.

Specific or Regulatory TFs Mechanism

Specific TFs interact with DNA sequences (enhancers or silencers) through their DNA-binding domain.
They interact with general TFs and RNA polymerase at the initiation complex through their protein-binding domain.
Coactivator proteins like histone acetyltransferase (HAT) interact via their transcription activation domain.

Bending of DNA Molecule

DNA bending allows interactions between specific TFs (bound to enhancer/silencer sequences) and basal TFs and RNAP located at the promoter region.

Regulation of Transcription by Epigenetic Mechanisms (DNA Accessibility)

A- Chromatin Remodeling: Acetylation and Deacetylation of histones alter the DNA-histone interaction and influences accessibility.
B- DNA Methylation: Alters DNA accessibility by adding methyl groups to cytosines, often within promoter regions. This can either hinder or enhance accessibility during transcription.

Euchromatin and Its Effect on Transcription

Following acetylation and nucleosomal removal, the promoter is opened.
Transcription machinery can access the promoter, leading to active transcription.

mRNA Posttranscriptional Level Regulation

1. Splice-site choice: Alternative splicing of mRNA molecules (discussed before).
2. mRNA editing: Modifications to mRNA after processing.
3. Coordinate expression: Coordination of gene expression in eukaryotes.
4. mRNA stability: Regulation of mRNA lifespan.

2. The Editing of mRNA

Two different-sized Apo B proteins are produced: Apo B-100 (full length, in the liver) and Apo B-48 (smaller, in the intestine).

3. Co-ordinated Expression in Eukaryotes

Cell surface hormones like glucagon initiate a signaling pathway involving cAMP, protein kinase A, and CREB.

4. mRNA Stability Regulation

Transferrin (an iron transport protein) is regulated via its mRNA stability in response to iron concentration.

1. DNA accessibility: Influenced by chromatin remodeling and DNA methylation to facilitate transcription factors' access to DNA sequences.
2. DNA copy number: Gene amplification affects the amount of DNA.
3. DNA rearrangements: Rearrangement of DNA segments allows for immune responses (immunoglobulins), impacting variety.
4. DNA mobile elements (transposons): Can affect gene expression and have implications in human diseases. DNA rearrangements during immunoglobin creation generates a high diversity of antibodies.

References for Further Readings

Lippincott Illustrated Review Integrated System
Lippincott Illustrated Review 6th edition
Oxford Handbook of Medical Science 2nd edition
Clinical Key Student

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Test your knowledge on gene regulation and expression with this quiz. Explore topics such as promoter sequences, enhancer and silencer elements, and the role of hormones and proteins in gene expression mechanisms. Perfect for students of molecular biology and genetics.