Translation And Regulation Flashcards
What makes up eukaryotic ribosomes
80s ribosome 40 ss, 60 ls. 18s rRNA,28s rRNA, 5.8,5 LS has 50 proteins Ss has 33 proteins
What is the catalytic subunit of ribosome
Rna
What gets transferred to trnas via trna synthetase
Amino acid + adenosine tp (2ppi lost for energy)
= amino adenylate = amino acyl trna
Why is ribosomal rna needed
Peptide bond formation is unfavourable
What are the 3 sites on the 40s subunit
EPA
Exit
Polypeptide chain site
Amino acyl trna bs
What sequence is scanned by the ribosome around the aug start
Kozak consensus
Does small subunit 40 bind to cap for initiation
Yes
What needs to happen structurally to mrna for initiation
Circularisation by bringing cap and poly a together
What complex is responsible for initiation
Eif4 complex (g,e,a)
What eif4 binds to the cap
Eif4 E
What does eif4 G bind
Eif4 A, 3 and poly A binding proteins and E (circularising mrna)
What does eif4 A have
ATPase and rna helicase
What is the eif2 complex
Eif2 gtp, attached to trna met (start trna)
What does eif2 complex associate with first in translation
43s pic
Recycled 40s subunit, eif 1a,1 and 3
Once the 43s is attached to the eif2 trna complex. What attaches
The eif4 E binds to cap, eif4G binds to pabp,3, and E causing circularisation
Once the 43s binds with the eif4 complex around the cap, what happens
Can scan the start codon and kozak
What happens when start codon is scanned
Eif2 gtp is hydrolysed, the 43s binds with the eif4 complex and eif2complex.
= 48s initiation complex
Trna met can join via anticodon
What allows the 60s subunit to bind
Eif5b GTP hydrolysis. This occurs when the 48s initation complex is attached to start codon
What happens to eif when 60s binds
All leave at different times
What allows elongation by bringing a new amino acyl trna to the A site
Ef G 1a and gtp hydrolysis
Then allows translocation
What is peptide forming called
Peptides transferase reaction (via rna catalism )
Which release factor binds stop codon in A site
Erf1
Which release fsctor cleaves peptide chain from trna
Erf3 gtp hydrolysis
after erf3 hydrolysis, what is released and recycled
Ribosomes, trna released
The 40s stays with 1,1a and 3 forming the 43s pic
How is EIF2 used to regulate translation
It is phosphorylsted which stops it’s action - means no gtp hydrolysis of eif2 = no start codon recognition and no 48s initation complex
When is eif2 inactivated
Eg due to amino acid shortage or cell stress
What dephosphorylates eif2 activating it
Growth factors
How can eif2 regulation be used to switch only mrna to do with stress eg heat shock on for translation
Via distinctive elements on mrna which identifies them
How does level of irons impact
They regulate expression of transporters of iron or storage of iron if too high
What are UTRs
Untranslated regions on mrna
5’ Utr Is between cap and start codon (binding blocks ribosome scanning)
3’ is between stop codon and poly A (for stability)
What happens in low iron levels
Mrna for transporters is up regulated to get more iron
This is via IRP1 binding to the 3’ utr for stability = more expression
IRP1 binds to 5’ utr on storage mrna = blocked translation
What does IRP1 bind to on rnas
IREs
In high iron levels, the iron binds to IRP1, how does this have effect on storage mrna
It means IRP1 can’t block translation of storage mrna because can’t bind to 5’ utr = translated
Also means it can’t stabilise at 3’ utr for the transporter mrna = unstable and degraded
What does bi functionality of IRP1 mean
When it’s bound to iron it changes it’s role to a c aconitase
