Eukaryotic Gene Expression Quiz

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Questions and Answers

What is the primary role of RNA molecules in eukaryotic gene expression?

To carry genetic information from DNA to the ribosomes (correct)

To provide structural support to the cell

To replicate DNA

To digest cellular waste

Which process is crucial for the synthesis of RNA in eukaryotic cells?

Translation

Transcription (correct)

Replicative transcription

Protein folding

How does post-transcriptional control affect gene expression in eukaryotic cells?

It increases the number of chromosomes in the cell

It modifies RNA after synthesis, affecting the availability of mRNA for translation (correct)

It alters DNA structure to prevent replication

It blocks transcription entirely

What characteristic of eukaryotic DNA organization prevents tangling while allowing accessibility for gene expression?

Complex chromosomal packaging Signup and view all the answers

Which types of regulatory molecules are essential for controlling transcription in eukaryotic cells?

Transcription factors Signup and view all the answers

What role does TFIID play in the transcription initiation process?

It distorts local DNA structure allowing TFIIB to bind. Signup and view all the answers

Which general transcription factor is responsible for exposing the template strand?

TFIIH Signup and view all the answers

What is required for RNA polymerase to be released from general transcription factors?

Phosphorylation of its polypeptide tail by TFIIH. Signup and view all the answers

During transcription initiation, what happens after the formation of the transcription initiation complex?

Elongation factors load onto RNA polymerase for active transcription. Signup and view all the answers

What is the significance of the energetically unfavorable reaction during transcription initiation?

It couples with ATP hydrolysis to facilitate strand separation. Signup and view all the answers

What is the primary role of RNA polymerase in transcription?

It unwinds the DNA helix and catalyzes the formation of phosphodiester bonds. Signup and view all the answers

Which of the following bases is found in RNA but not in DNA?

Uracil Signup and view all the answers

Which RNA polymerase is primarily responsible for synthesizing most types of RNA?

RNA polymerase II Signup and view all the answers

What is the function of the TATA box in transcription?

It is a promoter region that facilitates the binding of transcription factors and RNA polymerase. Signup and view all the answers

How do ribose and deoxyribose differ?

Ribose contains one more oxygen atom than deoxyribose. Signup and view all the answers

What role do transcription factors play in the initiation of transcription?

They assemble on the promoter to orient RNA polymerase and initiate transcription. Signup and view all the answers

What is a key difference between the structure of RNA and DNA?

RNA contains uracil, whereas DNA contains thymine. Signup and view all the answers

Which factor is NOT a role associated with RNA besides mRNA?

Storing genetic information. Signup and view all the answers

What is the primary role of capping and polyadenylation in eukaryotic mRNA?

To increase stability of mRNA and facilitate export to cytosol Signup and view all the answers

What are exons primarily known for in eukaryotic genes?

They are short protein-coding sequences scattered throughout the gene Signup and view all the answers

Which of the following best describes the function of snRNAs in splicing?

They act as ribozymes that catalyze splicing reactions Signup and view all the answers

What is the role of splice junction complexes?

They indicate successful completion of splicing Signup and view all the answers

How are introns removed from pre-mRNA?

Through the formation of a lariat structure Signup and view all the answers

What must occur before pre-mRNAs can be exported for protein translation?

Introns must be removed and exons stitched together Signup and view all the answers

What signals the beginning and end of an intron in pre-mRNA?

snRNPs recognizing splice-site sequences Signup and view all the answers

What is the consequence of failed mRNA export from the nucleus?

The mRNA will accumulate in the nucleus and degrade Signup and view all the answers

What is the primary function of the nuclear pore complexes?

To mediate the export of mRNA to the cytosol Signup and view all the answers

Which proteins are required for the export of mRNA from the nucleus?

Poly-A-binding proteins, cap-binding complex, and exon junction complexes Signup and view all the answers

What role do transcription regulators play in gene expression?

They can either activate or repress transcription Signup and view all the answers

How can regulatory DNA sequences influence gene expression?

Through integration of various environmental signals Signup and view all the answers

What is a potential consequence of allowing aberrantly spliced transcripts to leave the nucleus?

They can become harmful Signup and view all the answers

What mechanism facilitates interaction between transcriptional machinery and the promoter?

Formation of a Transcription Initiation Complex (TIC) Signup and view all the answers

What is the role of repressor proteins in gene transcription?

To inhibit the assembly of the TIC or block RNA polymerase progression Signup and view all the answers

What happens to waste RNAs that remain in the nucleus?

They are degraded and can be reused for transcription Signup and view all the answers

What determines the transcription rate of eukaryotic genes?

Combinations of transcription regulators Signup and view all the answers

What is a role of post-transcriptional controls in eukaryotic cells?

To fine-tune gene expression after transcription initiation Signup and view all the answers

How does alternative RNA splicing benefit eukaryotic cells?

It allows for the production of different mRNAs and proteins from one gene Signup and view all the answers

The presence of repressor proteins in the 5' UTR region primarily affects which process?

Ribosome access to mRNA Signup and view all the answers

What is the significance of mRNA lifespan in protein expression levels?

Longer mRNA lifespan allows for multiple translations of the same mRNA Signup and view all the answers

Which mechanism helps control mRNA degradation in eukaryotic cells?

The presence of specific binding sites for degradation factors Signup and view all the answers

What is an outcome of combinatorial control in gene expression?

Specific gene expression in response to various signals Signup and view all the answers

Which statement accurately describes the role of a single protein in gene expression?

It can coordinate the expression of multiple genes. Signup and view all the answers

Study Notes

Gene Expression in Eukaryotic Cells

Course: SBP3411
Instructor: Dr. Hanis H. Harith
Department of Biomedical Science, UPM

Learning Outcomes

Identify the role of different types of RNA molecules in eukaryotic gene expression
Describe the key events and molecules involved in RNA synthesis and processing in eukaryotic cells
Discuss the role of transcription regulators in eukaryotic gene expression
Describe examples of mechanisms of post-transcriptional control at different levels

Lecture Outline

Types of RNA & RNA polymerases
RNA synthesis and processing
Transcriptional controls
Post-transcriptional controls

DNA Organization in Eukaryotic Cells

Storage of hereditary information
All cell types in a multicellular organism contain the same DNA content
Eukaryotic DNA is packaged into multiple chromosomes
Chromosome packing occurs on multiple levels, preventing tangling while remaining accessible for replication, repair, and gene expression.

Flow of Genetic Information

Genetic information flows from DNA to RNA (transcription) and from RNA to protein (translation)
DNA is transcribed into RNA, which is then translated into a protein.
The sequence of DNA determines the sequence of RNA, which in turn determines the sequence of amino acids in the protein.
Segments of DNA that are transcribed into RNA are called genes.
Non-coding sequences (introns) are spliced out from pre-mRNA.

RNA Transcripts or Molecules

RNA carries information from the DNA
RNA has different chemical forms (ribose vs. deoxyribose; uracil vs. thymine).
RNA polymerase unwinds DNA, creating phosphodiester bonds between nucleotides.
Different types of RNA have different functions, such as messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA).

RNA Synthesis in Eukaryotic Cells: Initiation

General transcription factors (TFs) are assembled on the promoter region of a gene.
Promoter: DNA sequences upstream of transcription start site (+1).
TFIID binds to the TATA box (located at -30).
TATA box is common on promoters used by RNA polymerase II.
Local DNA distortion by TFIID allows adjacent binding of TFIIB.

RNA Synthesis: Formation of Transcription Initiation Complex

Assembly of other general TFs exposes the template strand (ATP hydrolysis required).
Binding of RNA polymerase completes the formation of the transcription initiation complex.
RNA polymerase needs to be released from most general TFs (phosphorylation of RNA polymerase by TFIIH occurs).

RNA Synthesis: Elongation & Termination

Elongation factors facilitate movement of RNA polymerase.
Polynucleotide synthesis is driven by ATP hydrolysis.
Incoming ribonucleoside triphosphates react with the 3' end of the RNA chain.
Hydrolysis of pyrophosphate drives overall reaction towards polynucleotide synthesis.
When transcription ends, RNA polymerase is dephosphorylated by protein phosphatases and released from DNA.

Eukaryotic RNA Processing: RNA Capping & Polyadenylation

RNA processing (capping, splicing, polyadenylation) occurs as RNA is synthesized.
Facilitated by enzymes on the phosphorylated tail of RNA polymerase.
RNA capping: attachment of a guanine nt with a methyl group at the 5' end when RNA transcript is about 25 nts long
Polyadenylation: addition of adenine nucleotides to form poly-A tail at the 3' end.
Significance of capping and polyadenylation increases mRNA stability and facilitates export.

Organization of Eukaryotic Genes and Pre-mRNA

Exons are short protein-coding sequences.
Introns are long, non-coding sequences.
Both exons and introns are transcribed into pre-mRNA.
RNA splicing removes introns and joins exons.
RNA splicing and processing are required for pre-mRNAs to become functional mRNA.

RNA Splicing by Spliceosome

The core of the spliceosome is composed of snRNAs and proteins (snRNPs).
snRNAs act as ribozymes that catalyze the splicing reactions.
Successful splicing is marked by exon junction complexes.
snRNPs recognize splice-site sequences signaling the beginning and end of introns by complementary base pairing.
Introns are spliced out by forming a lariat structure, then degraded.

mRNA Export

Only correctly processed mRNAs are exported to the cytosol.
Bound to poly-A-binding proteins, a cap-binding complex, and exon junction complexes.
Mediated by nuclear pore complexes.
Waste RNAs remain and are degraded.

Gene Expression is Mainly Controlled by Transcription Regulators

Transcription regulators switch transcription on/off (activator/repressor).
Proteins recognize specific regulatory DNA sequences and form noncovalent interactions.
Regulatory DNA sequences integrate information from many signals.

Transcription Regulators can Recruit Chromatin-Modifying Proteins

DNA packaging (e.g., nucleosomes) can physically block assembly of the transcription initiation complex (TIC).
Chromatin structure needs modification to access promoters.
Gene activators enhance transcription initiation efficiency by recruiting enzymes that covalently modify histone proteins (e.g., HATs).
Proteins including general transcription factors promote transcription.
Chromatin remodeling complexes increase accessibility to nearby DNA (e.g., TATA box).
Gene repressors reduce transcription initiation efficiency by recruiting enzymes that modify histone proteins (e.g., HDACs).

Transcriptional Control in a Multicellular Organism

Some proteins are commonly expressed across cell types.
Distinctive cell properties are determined by expression of specialized proteins.
Expression of eukaryotic genes is controlled by combinations of transcription regulators (combinatorial control).
Multiple transcription regulators bind to respective regulatory DNA sequences.
Regulatory DNA sequences integrate information from various signals to determine transcription rate.
A single protein can coordinate the expression of multiple genes.

Post-transcriptional Controls in Eukaryotic Cells

Mechanisms operate after transcription initiation to fine-tune gene expression.
Alternative RNA splicing: Exons may be skipped or included by spliceosome, but their order in the DNA sequence is maintained.
Presence of binding sites for repressor proteins in the 5' UTR region.
Mechanisms control mRNA degradation or sequestering from mRNA.

Mechanisms of mRNA Degradation Control

mRNA lifespan determines protein expression level.
mRNA stability varies depending on nucleotide sequence (e.g., 3' UTR, which may contain binding sites for proteins involved in RNA degradation).
mRNAs are eventually degraded by RNases in the cytosol.
mRNA degradation can also be regulated by miRNAs.
miRNAs form RNA-induced silencing complex (RISC) in the cytosol and target specific mRNA with complementary sequences.
Target mRNA is rapidly degraded by RISC, or sequestered and degraded by nucleases.

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Description

Test your knowledge on the critical roles of RNA molecules in eukaryotic gene expression. This quiz covers topics such as transcription initiation, post-transcriptional control, and regulatory mechanisms essential for controlling transcription. Check your understanding of key components involved in these processes!