Gene Expression Quiz

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Questions and Answers

What defines the difference in the type of mRNA produced in prokaryotes compared to eukaryotes?

Prokaryotes produce shorter mRNAs.

Eukaryotic mRNAs are often monocistronic. (correct)

Prokaryotic mRNAs undergo extensive processing.

Eukaryotes produce polycistronic mRNAs.

Which element is crucial for the low-level transcription of a eukaryotic gene?

Enhancers

Silencers

TATA box (correct)

Introns

In eukaryotic gene expression, what is the role of enhancers?

To bind tissue-specific transcription factors. (correct)

To inhibit transcription.

To provide low transcription initiation.

To process mRNA transcripts.

During early cellular development, eukaryotic promoters are described as being what?

Bivalent or poised. Signup and view all the answers

How do introns affect the coding region of eukaryotic genes?

They are non-coding sequences within the mRNA. Signup and view all the answers

What distinguishes the regulation of eukaryotic gene expression from prokaryotic gene expression?

Eukaryotic genes often exhibit complex regulatory networks. Signup and view all the answers

Which of the following statements is true regarding eukaryotic core promoters and their surrounding elements?

Core promoters cannot operate in nucleosome-containing regions. Signup and view all the answers

What is a common feature of the promoters found in the human genome?

Most are associated with CpG islands. Signup and view all the answers

What is the primary role of CPSF in mRNA processing?

Polyadenylation of the 3' end Signup and view all the answers

How does alternative splicing increase the diversity of proteins?

By producing different isoforms from the same gene Signup and view all the answers

What is a consequence of mRNA processing in eukaryotic cells?

Protection of mRNA from exonucleases Signup and view all the answers

What is the size difference between eukaryotic and prokaryotic ribosomes?

Eukaryotic ribosomes are larger Signup and view all the answers

Where does translation primarily occur in eukaryotic cells?

In the cytoplasm Signup and view all the answers

What does polyadenylation do to the mRNA molecule?

It adds adenine nucleotides to the 3' end Signup and view all the answers

What is the role of introns during mRNA processing?

Non-coding sequences that are removed from the mRNA Signup and view all the answers

What can be inferred about the DSCAM gene in terms of its splicing capability?

It can produce over 38,000 different mRNA and protein combinations Signup and view all the answers

What is the correct flow of genetic information as indicated?

Gene > mRNA > protein Signup and view all the answers

Which statement best describes the role of the 5' Cap in mRNA?

It facilitates the attachment of ribosomes during initiation. Signup and view all the answers

What are housekeeping genes characterized by?

They will be constitutively expressed. Signup and view all the answers

Which component is found in both prokaryotic and eukaryotic gene structures?

Promoter Signup and view all the answers

What type of signals regulate transcription?

Both internal and external signals. Signup and view all the answers

How do aminoacyl-tRNA synthetases function in eukaryotic cells?

They attach correct amino acids to tRNA. Signup and view all the answers

What is the significance of the polyadenylylation signal sequence in mRNA?

It signals the addition of a polyA tail. Signup and view all the answers

What are polyribosomes primarily associated with?

The synthesis of proteins. Signup and view all the answers

Study Notes

Gene Expression

Prokaryotes: Transcription occurs in the cytoplasm, translation occurs in the cytoplasm, mRNA is often polycistronic, 5' UTR and 3' UTR are shorter than in eukaryotic mRNA, no mRNA processing, no introns.
Eukaryotes: Transcription occurs in the nucleus, translation occurs in the cytoplasm, mRNA is monocistronic, 5' UTR and 3' UTR are longer than in prokaryotic mRNA, mRNA processing with splicing of introns, complex regulatory networks and TADs (Topologically Associating Domains).

Structure of Eukaryotic Gene

Core Promoter:
- ~100 bp, contains TSS (Transcription Start Site): TATA box, CAAT box, GC box.
- Binds general transcription factors, resulting in low transcription levels.
Proximal & Distal Promoters:
- Up to several Kbp (kilobase pairs) away from the core promoter.
- Enhancers bind tissue-specific transcription factors leading to high expression.
- Insulators bind insulator proteins to define TAD boundaries.
- Silencers bind repressor proteins to inhibit transcription.
Active Promoters:
- Are located in nucleosome-free zones.
- Flanking nucleosomes possess active or repressed epigenetic marks.
- During early development, promoters are bivalent/poised and can become active or inactive as the cell differentiates.
Mammalian Genes:
- Often have two or more alternate promoters.
- Respond to different regulatory elements.
- Allow the production of protein isoforms.
CpG Islands:
- Found in 70% of human promoters and lack most core promoter elements.

RNA Coding Region

Contains one or more introns.
Starts with an exon containing the start codon.
Ends with an exon containing the stop codon.
RNA transcripts undergo post-transcriptional processing.
No clear transcription termination sequence.
Determined during RNA processing: Cleavage occurs 15-30 nucleotides (nt) downstream of the PAS (polyadenylation signal).

mRNA Processing

5' Cap:
- Protects mRNA from exonucleases.
- Aids mRNA transport to the cytoplasm.
- Facilitates binding to the 40S ribosomal subunit.
PolyA Tail:
- Aids mRNA transport to the cytoplasm.
- Facilitates binding to the ribosome.
Intron Splicing:
- Removal of introns from pre-mRNA.
- Promotes export of mature mRNA from the nucleus.
- Prevents degradation of mature mRNA.

Eukaryotic Transcription: Termination

CPSF (Cleavage and Polyadenylation Specificity Factor):
- Recognizes the PAS.
- Cleaves the pre-mRNA downstream of the PAS.
PAP (PolyA Polymerase):
- Adds a poly(A) tail to the 3' end of the mRNA.

Alternative Splicing

Different isoforms of proteins can be produced from the same gene.
Produces diverse protein products from a single gene.

Eukaryotic Translation

Requires more factors than prokaryotic translation.
The eukaryotic ribosome is larger than the prokaryotic ribosome.
Translation occurs in the cytoplasm.
Eukaryotic translation is highly regulated, particularly at the initiation stage.
Eukaryotic translation elongation and termination resemble prokaryotic translation.

Eukaryotic Gene Expression - Regulation of Transcription

Internal Cellular Signals:
- DNA binding factors (transcription factors).
- Chromatin state (euchromatin vs heterochromatin).
- Transcription machinery (RNA polymerase, general transcription factors).
External/Environmental Signals:
- Hormones
- Cellular stress
Complex Interplay:
- A complex interplay of internal and external signals governs gene expression.

Regulatory Elements

Housekeeping Genes:
- Are constitutively expressed (always on).
Other Genes:
- Have specific temporal-spatial expression (regulated expression in specific times and locations).

Prokaryote vs. Eukaryote mRNA

Prokaryotic mRNA:
- Polycistronic (encodes multiple proteins).
- Shorter 5' and 3' UTR.
- No introns.
Eukaryotic mRNA:
- Monocistronic (encodes a single protein).
- Longer 5' and 3' UTR.
- Introns are present.
5' Cap:
- Aids ribosomal binding and protection from degradation for both prokaryotes and eukaryotes, but plays a more prominent role in eukaryotic mRNA stability.
PolyA Tail:
- Important for both prokaryotic and eukaryotic mRNA stability and translation, but plays a more prominent role in eukaryotes and functions as a signal for mRNA termination.
Introns:
- Present only in eukaryotic mRNA.
- Removed via splicing to produce a mature mRNA molecule.

5' Cap and PolyA Tail

Both 5' cap and polyA tail help the mRNA engage in the eukaryotic ribosome binding site (RBS).

Summary

Prokaryotes and eukaryotes share some similarities in gene expression, but eukaryotes have more complex regulatory mechanisms.
Eukaryotic gene expression is regulated by internal and external signals, which control when and where genes are expressed.
Alternative splicing is a unique feature of eukaryotic gene expression, generating different isoforms of proteins from the same gene.

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Description

Test your knowledge on gene expression mechanisms in prokaryotes and eukaryotes. This quiz covers transcription, translation, mRNA characteristics, and the structure of eukaryotic genes, including core and distal promoters. Challenge yourself with questions about the differences in gene expression between these two types of organisms.