T.14 rRNA

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Questions and Answers

What is the primary function of the large subunit in ribosomal RNA?

To bind to mRNA during translation

To provide the platform for mRNA translation (correct)

To regulate gene expression

To catalyze peptide bond formation

What is the purpose of cleavage during rRNA processing?

To add methyl groups to specific residues

To remove external transcribed spacers and internal transcribed spacers (correct)

To remove excess nucleotides

To isomerize uridine residues to pseudouridine

What is the role of upstream binding factor (UBF) in rRNA transcription?

To catalyze peptide bond formation

To bind to the rRNA promoter, enhancing transcription (correct)

To bind to the rRNA promoter, inhibiting transcription

To regulate rRNA processing and modification

What is the consequence of rRNA playing a central role in protein synthesis?

The platform for mRNA translation is provided Signup and view all the answers

What is the characteristic of rRNA genes in terms of organization?

They are organized in multiple tandem repeats Signup and view all the answers

What is the process by which rRNA synthesis occurs?

Repeats-in-tandem transcription Signup and view all the answers

What is the primary location where the biogenesis of eukaryotic ribosomes takes place?

Nucleolus Signup and view all the answers

What is the approximate number of proteins involved in the complete processing of ribosomes?

Around 200 proteins Signup and view all the answers

Which RNA polymerase is responsible for transcribing the 5S rRNA?

RNA pol III Signup and view all the answers

What type of RNA is transcribed by RNA pol II in the context of ribosome biogenesis?

mRNA Signup and view all the answers

Where are the ribosomal proteins translated?

Cytoplasm Signup and view all the answers

At what stage do the ribosomal proteins bind to the pre-60S subunit?

After transcription Signup and view all the answers

What is the role of snoRNPs in the modification of rRNA?

To guide enzymes to specific sites for modification Signup and view all the answers

What is the purpose of the U3 snoRNA in the modification of rRNA?

To orchestrate the endo- and exonucleolytic cuts of rRNA Signup and view all the answers

What is the consequence of the lack of modifications in rRNA?

The ribosome becomes less efficient in protein synthesis Signup and view all the answers

What is the typical location of the modifications in mature rRNA?

In the conserved domains of the rRNA Signup and view all the answers

What is the function of the FIB protein in snoRNP complexes?

To act as a 2'-O-methyltransferase Signup and view all the answers

What is the effect of pseudouridilation on rRNA structure?

It affects the hydrogen bonding in rRNA Signup and view all the answers

What is the function of the Cbf5 protein in snoRNP complexes?

To act as a pseudouridine synthase Signup and view all the answers

What is the consequence of having multiple snoRNA molecules?

Each snoRNA molecule guides multiple modifications Signup and view all the answers

What is the characteristic of snoRNA molecules?

They have a specific secondary structure Signup and view all the answers

What is the number of pseudouridylations in mature rRNA?

Between 43 and 100 Signup and view all the answers

What occurs in the nucleoplasm?

Exit of ribosomal subunits to the cytoplasm Signup and view all the answers

What is the result of the biogenesis of ribosomes?

fabrication of proteins in large quantities Signup and view all the answers

What is the function of the U3 snRNP?

cleaving of precursor rRNA Signup and view all the answers

What is unique about the 5'8S rRNA?

it is part of the 25S rRNA in eubacteria Signup and view all the answers

What is the role of the SSU procesoma?

processing of precursor rRNA Signup and view all the answers

What is the consequence of inefficient ribosomal biogenesis?

impaired cellular growth Signup and view all the answers

What is the characteristic of snoRNAs?

they are small and localized to the nucleolus Signup and view all the answers

What is the result of the cleavage of precursor rRNA?

formation of mature rRNA Signup and view all the answers

What is the function of nucleases in rRNA processing?

cleavage of precursor rRNA Signup and view all the answers

What is the significance of the biogenesis of ribosomes?

it is essential for cellular growth Signup and view all the answers

Study Notes

Structure

rRNA (ribosomal RNA) makes up a large part of the ribosome, the cell's protein synthesis machinery
Consists of two main components:
- Large subunit (LSU): 23S rRNA in prokaryotes, 25S-28S in eukaryotes
- Small subunit (SSU): 16S rRNA in prokaryotes, 18S in eukaryotes
rRNA is highly conserved across species, with modifications and methylation occurring post-transcriptionally

Processing

rRNA transcription occurs in the nucleolus, a region within the nucleus
Primary transcript (pre-rRNA) undergoes several processing steps:
- Cleavage: removal of external transcribed spacers (ETS) and internal transcribed spacers (ITS)
- Trimming: removal of excess nucleotides
- Methylation: addition of methyl groups to specific residues
- Pseudouridylation: isomerization of uridine residues to pseudouridine
Mature rRNA is assembled into the ribosome

Regulation

rRNA transcription is regulated by various factors, including:
- RNA polymerase I: responsible for transcribing rRNA genes
- Selectivity factor 1 (SL1): binds to the rRNA promoter, enhancing transcription
- Upstream binding factor (UBF): binds to the rRNA promoter, enhancing transcription
- Nucleolar proteins: regulate rRNA processing and modification
Regulation can occur at the transcriptional, post-transcriptional, and translational levels

Function

rRNA plays a central role in protein synthesis:
- Provides the platform for mRNA translation
- Binds to mRNA and tRNA during translation
- Catalyzes peptide bond formation
rRNA also plays a role in:
- Ribosome assembly and stability
- Regulation of gene expression
- Cellular stress response

Synthesis

rRNA genes are organized in tandem repeats, with each repeat containing:
- A promoter region
- A 5' external transcribed spacer (ETS)
- The 18S, 5.8S, and 25S/28S rRNA genes
- A 3' ETS
rRNA synthesis occurs through a process called "repeats-in-tandem transcription"
RNA polymerase I transcribes the rRNA genes, producing a long primary transcript that undergoes processing and modification to produce mature rRNA

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Description

Explore the structure, processing, regulation, and function of ribosomal RNA (rRNA), including its role in protein synthesis and cellular processes. Learn about the different components of rRNA, its transcription, processing, and modification, and its regulation in cells.