Gene Expression and Epigenetics Quiz

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Questions and Answers

Which statement correctly describes the role of activator proteins?

They facilitate transcription by attracting histone acetyl transferases. (correct)

They permanently condense chromatin to regulate gene expression.

They block transcription by binding to enhancer regions.

They recruit histone de-acetylase enzymes to tighten DNA packing.

How do repressor proteins inhibit gene transcription?

By increasing the availability of enhancers for transcription.

By binding to promoter regions and blocking transcription factors. (correct)

By promoting the formation of euchromatin for gene activation.

By attracting histone acetyl transferases to enhance chromatin accessibility.

What is a significant outcome of X-chromosome inactivation?

It causes one X chromosome to condense into heterochromatin, deactivating it. (correct)

It leads to the transcription of both X chromosomes simultaneously.

It increases the dosage of genes expressed from the active X chromosome.

It enhances the transcription of genes on both X chromosomes.

What happens when histone acetyl groups are removed from histone proteins?

It reduces the rate of transcription by making DNA more tightly packed. Signup and view all the answers

What is meant by dosage compensation in the context of X-chromosome inactivation?

It refers to equalization of gene expression from both active X chromosomes. Signup and view all the answers

What is the primary function of the TATA box in transcription?

To serve as a binding site for RNA polymerase II Signup and view all the answers

Why does RNA polymerase II not require a primer for transcription?

It is inherently capable of initiating transcription at the promoter Signup and view all the answers

Which of the following accurately describes the direction of RNA synthesis during transcription?

RNA is synthesized from 5' to 3' while moving 3' to 5' on the template Signup and view all the answers

What is the effect of the RNA capping process on mRNA?

It enhances the stability and translational efficiency of mRNA Signup and view all the answers

Which of the following is NOT a component involved in the action of RNA polymerase II during transcription?

Ribosomes Signup and view all the answers

How does RNA polymerase II detach from the DNA strand during transcription?

Upon reaching the terminator sequence Signup and view all the answers

Which statement correctly describes the structural differences between RNA and DNA?

RNA contains uracil instead of thymine and is single-stranded Signup and view all the answers

What role do general transcription factors play in the process of transcription?

Enabling RNA polymerase II to recognize the correct template strand Signup and view all the answers

What is the primary role of polyadenylation in mRNA processing?

To increase the stability of mRNA Signup and view all the answers

During splicing, which structures are primarily responsible for the removal of introns?

snRNPs Signup and view all the answers

What is the effect of a frameshift mutation caused by an insertion or deletion?

It alters the reading frame, affecting downstream amino acids. Signup and view all the answers

Which of the following describes the role of tRNA during translation?

It recognizes complementary codons on the mRNA through its anticodon. Signup and view all the answers

What defines the start codon in the genetic code?

It codes for methionine and signals the initiation of translation. Signup and view all the answers

How do enhancers affect gene expression?

They can increase transcription rates even from distant locations. Signup and view all the answers

What is the function of peptidyl transferase in ribosomes?

To catalyze the formation of peptide bonds Signup and view all the answers

Which component of the ribosome binds to the mRNA during translation?

30s small subunit Signup and view all the answers

Study Notes

Gene Expression and Epigenetic Mechanisms

Gene expression is the utilization of DNA information to form proteins or RNA with structural, regulatory, or catalytic roles.

Transcription

Initiation:
- Genes have a promoter sequence before the coding region, containing a TATA box rich in adenine and thymine bases.
- General transcription factors bind to the TATA box, allowing RNA polymerase II to attach and begin transcription.
- RNA polymerase II does not require a primer, unlike DNA replication.
- It ensures the correct template strand is transcribed.
RNA Polymerase II Action:
- RNA is synthesised 5' to 3' (RNA polymerase travels 3' to 5' on the template strand).
- DNA double helix is unwound segmentally.
- RNA polymerase forms phosphodiester bonds between triphosphate nucleotides (ATP, CTP, GTP, UTP) complementary to the template strand.
- Transcription continues until a terminator sequence is reached.
- The mRNA transcript extends through the terminator sequence but not the promoter, differing from DNA.

mRNA Modification

RNA Capping: A guanine nucleotide is added to the 5' end, enhancing mRNA stability and nuclear export.
Polyadenylation: A series of adenine nucleotides are added to the 3' end for stability and export.
Splicing: Introns are removed by spliceosomes (snRNA and accessory proteins), reconnecting coding exons.
Alternative splicing: Different splicing patterns can create multiple proteins from a single gene.

Translation

Genetic Code: Three-base codons specify amino acids. 64 possible codons for 20 amino acids, with redundancy. The start codon (AUG) codes for methionine and signals initiation. Stop codons (UAA, UAG, UGA) signal termination.
Mutations:
- Insertions/Deletions: Alter the reading frame, potentially affecting the entire protein. A multiple of 3 nucleotide insertion/deletion does not result in a frameshift mutation
- Substitutions: Incorrect base substitution, potentially altering the final amino acid. The effect depends on the location and nature of the base change.
tRNA: Transfer RNA (tRNA) molecules have complementary anti-codons to bind with mRNA codons. Aminoacyl-tRNA synthetase enzymes attach amino acids to tRNA.
Ribosomes:
- Ribosomes (50S and 30S subunits) bind mRNA.
- tRNA binding sites (E, P, A) are crucial for protein synthesis.
Translation Process:
- Methionyl-tRNA initiates at the start codon (AUG).
- A second tRNA complementary to the next codon binds to the A site.
- Peptidyl transferase forms a peptide bond.
- The first tRNA moves to the E site, exiting.
- The process repeats to synthesize the entire protein sequence until the stop codon is reached.
- Multiple ribosomes can translate the same mRNA, accelerating protein production.

Regulation of Gene Expression

Enhancers: DNA sequences that proteins can bind to, enhancing transcription rate. Their location (far distant from a gene) is overcome by DNA looping.
Activator proteins: Bind enhancers, increasing transcription rate by attracting histone acetylases.
Repressor proteins: Bind to the promoter, blocking transcription by attracting histone deacetylases.
Histone modifications: Acetylation loosens DNA packaging, activating transcription; deacetylation tightens DNA packaging, repressing transcription (enzymes involved are histone acetyl transferases and histone deacetylases respectively)
X-chromosome inactivation: A striking example of epigenetic repression, permanently inactivating one X chromosome to equalize gene expression in females.

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Description

Test your knowledge on gene expression and the epigenetic mechanisms involved in transcription. This quiz covers key concepts including the role of RNA polymerase II, the initiation of transcription, and the importance of promoter sequences. Improve your understanding of how genetic information is utilized in the formation of proteins and RNA.