Lecture 15 - Processing of tRNA and rRNA Flashcards
Principle characteristic of pockets of protein activity/activation
No membrane
Exemple of pocket of protein activity/activation in the nucleus and what happens there
Nucleolus : Transcription and processing of rRNA and tRNA
What plays an important role in pre-tRNA/pre-rRNA folding for further processing
Their untranslated regions
% of transcripts that are rRNAs in a proliferating cell and why
80% rRNA transcripts because need ribosomes -> effective translation
mRNA tends to distinguish ____________
cells from one another
tRNA and rRNA (so Pol I and Pol III) ensure the function of the ___________
transcription (and translation) machinery
Why do we say that rRNA acts similarly to snRNA and what does it do
Because interacts with a protein complex (and this complex will translate mRNA)
Where pre-tRNAs are processed (like cytoplasm …)
nucleoplasm
What are nuclear bodies
Functional specialized regions where interacting proteins form self-organized structures
On EM image, we can see nascent RNP. How/where is it visible and why
Visible at 5’ end of each pre-mRNA being transcribed because site of concentrated proteins (for capping in this case)
Large precursor pre-RNA transcribed by RNA Pol I -> what are the three kinds of changes it undergoes
Cleavage, exonuclease digestion, base-pair modifications
Large precursor pre-RNA : what its changes lead to
it yields mature 28 S, 18 S and 5.8 S rRNAs
What 28S, 18S and 5.8S RNAs associate with and where
With ribosomal proteins, in the nucleolus
What leads to the attraction of proteins together to form the nucleolus (what drives that, why do they do that)
Transcription (and therefore processing of rRNA, tRNA)
Proteins that gather to the nucleolus : what do they gather around and why
Around RNA to form a functional machine
To what extent 18S, 5.8S and 28S are preserved
Preserved in size across all types of eukaryotes
What is found on pre-rRNA (large precursor rRNA) from 5’ to 3’)
Preserved regions of rRNA (that are, from 5’ to 3’ : 18S, 5.8S, 28S) and between them, transcribed spacer regions
Transcribed spacer regions : conserved to what extend + their functions (2)
Not conserved.
Help for transcript folding and recognition by methylase or protein complexes required (function in maintenance of spatial dynamic)
Two main things that happen to pre-rRNA when processed
1) Complexes consisting of 70-80 prots attach and process the 5’ end
2) Sequence in the transcript is changed by methylation and pseudouridylation events
What directs the modifications of the pre-rRNA
snoRNPs (small nucleolar RNP)
How snoRNP recognizes pre-rRNA and what this ultimately leads to
Has specific regions/adresses that the protein complexes attached to pre-rRNA recognize and the snoRNP identifies certain residues in the transcript
3 known modifications that pre-rRNAs undergo at the snoRNP
Ribose methylation, pseudoudirylation and uridine-pseudouridine conversion
How many known conserved sequences in snoRNPs
none
When pre-rRNA is processed
As it is being transcribed
What part of the snoRNP recognizes the pre-rRNA and what part does the modifications
snoRNA part recognizes the pre-rRNA
Enzymes/Proteins of the snoRNP do the modifications
What happens during ribose methylation (attraction and how/why methylation occurs)
snoRNA makes a finger that attracts pre-rRNA : they base-pair. A methylase recognizes this structure due to the folding of the pre-rRNA due to presence of transcribed spacer regions.
What happens during pseudouridylation (attraction and how/why modif occurs)
snoRNA makes a finger with a hub in the middle : pre-rRNA hybridizes there.
Enzymes recognize this structure and will modify it
What happens (chemically) during uridine-pseudouridine conversion
An enzyme flips the C and the N
Modifications of tRNA (2) in the nucleus and how this is possible (what must happen during transcription)
1) Cleavage of 5’ end and 3’ end
2) Addition of CCA on 3’ end
2) Base modifications
Must be transcribed with extra parts
Why tRNAs have to be precise
Carry a specific amino acid and a specific anticodon
First 5’ end sequence found in tRNA : 2 functions
1) Folding of the tRNA
2) Recognition by tRNA synthetase
What happens to first 5’ end sequence in tRNA after doing its job
It is lost
What happens to excess nucleotides in the tRNA after transcription and folding
Excess nucleotides are degraded (it’s the reason why 5’ end sequence is gone/now shorter)
What happens to the 3’ end of the tRNA during processing
CCA tail is added (from 5’ to 3’)
What happens to residues within the stem loops of the tRNA during its processing + major event
Are replaced + lot of replacement in the anticodon loop with inosine by an enzyme complex
When can enzyme complexes interact with the anticodon loop of the tRNA
When the tRNA has a proper structure (this allows processing)
Basic principle of ribosome formation (what molecules are involved)
rRNA and tRNA with proteins form essential complexes of the ribosome
Summary of what happens during tRNA processing (3 things)
1) 5’ end for folding + tRNA synthetase recognition + is lost (excess residues removed)
2) 3’ end cleaved and CCA added at 3’ end
3) Residues in stem loops replaced + anticodon loop : major replacement with inosine involving enzyme complex
Principle purpose of intervening regions (3 things they do)
Help for folding, help for recognition by protein complexes + are lost afterwards
2 things protein complexes do for tRNA
Process it to make it functional and move it to the cytoplasm
Meaning of dark region on EM image (link with nuclear bodies)
More concentrated in proteins
What region of the tRNA will bind amino acids
CCA at 3’ end
