32 Questions
What is the primary function of the large subunit in ribosomal RNA?
To provide the platform for mRNA translation
What is the purpose of cleavage during rRNA processing?
To remove external transcribed spacers and internal transcribed spacers
What is the role of upstream binding factor (UBF) in rRNA transcription?
To bind to the rRNA promoter, enhancing transcription
What is the consequence of rRNA playing a central role in protein synthesis?
The platform for mRNA translation is provided
What is the characteristic of rRNA genes in terms of organization?
They are organized in multiple tandem repeats
What is the process by which rRNA synthesis occurs?
Repeats-in-tandem transcription
What is the primary location where the biogenesis of eukaryotic ribosomes takes place?
Nucleolus
What is the approximate number of proteins involved in the complete processing of ribosomes?
Around 200 proteins
Which RNA polymerase is responsible for transcribing the 5S rRNA?
RNA pol III
What type of RNA is transcribed by RNA pol II in the context of ribosome biogenesis?
mRNA
Where are the ribosomal proteins translated?
Cytoplasm
At what stage do the ribosomal proteins bind to the pre-60S subunit?
After transcription
What is the role of snoRNPs in the modification of rRNA?
To guide enzymes to specific sites for modification
What is the purpose of the U3 snoRNA in the modification of rRNA?
To orchestrate the endo- and exonucleolytic cuts of rRNA
What is the consequence of the lack of modifications in rRNA?
The ribosome becomes less efficient in protein synthesis
What is the typical location of the modifications in mature rRNA?
In the conserved domains of the rRNA
What is the function of the FIB protein in snoRNP complexes?
To act as a 2'-O-methyltransferase
What is the effect of pseudouridilation on rRNA structure?
It affects the hydrogen bonding in rRNA
What is the function of the Cbf5 protein in snoRNP complexes?
To act as a pseudouridine synthase
What is the consequence of having multiple snoRNA molecules?
Each snoRNA molecule guides multiple modifications
What is the characteristic of snoRNA molecules?
They have a specific secondary structure
What is the number of pseudouridylations in mature rRNA?
Between 43 and 100
What occurs in the nucleoplasm?
Exit of ribosomal subunits to the cytoplasm
What is the result of the biogenesis of ribosomes?
fabrication of proteins in large quantities
What is the function of the U3 snRNP?
cleaving of precursor rRNA
What is unique about the 5'8S rRNA?
it is part of the 25S rRNA in eubacteria
What is the role of the SSU procesoma?
processing of precursor rRNA
What is the consequence of inefficient ribosomal biogenesis?
impaired cellular growth
What is the characteristic of snoRNAs?
they are small and localized to the nucleolus
What is the result of the cleavage of precursor rRNA?
formation of mature rRNA
What is the function of nucleases in rRNA processing?
cleavage of precursor rRNA
What is the significance of the biogenesis of ribosomes?
it is essential for cellular growth
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
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.
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