Translation (Copeland) Flashcards
3’ UTR is site of
Key regulatory sequences
Stop codons
UGA, UAA, UAG
5; 7-methyl GMP cap is site of binding of
initiation factors
3’ CCA end of tRNA is not ___
Transcribed! It is added after processing
-need CCA end of enzyme can teach
Aminoacylation requires
ATP
Amino acyl tRNA synthetase
Recognizes tRNAs and adds appropriate amino acid
If incorrect amino acid is in the CCA 3’ site (synthesis site) it is moved to the
Editing site and removed
Eukaryotic ribosome properties
80S (60S + 40S)
-mostly RNA –> Ribozyme
-3 tRNA binding sites
5’ E P A 3’
Initiation and elongation occur
Simultaneously
-yield multiple ribosomes on single mRNA molecule –> V large complex “polysomes”
What is the most important for regulation of translation?
Initiation
- assembly of ribosome & mRNA
- positioning of ribosome on start codon
EIF2
Eukaryotic transcription factor
Binds & delivers initiator Met-tRNA
EIF4E
Binds 5’ cap
EIF4G
Scaffold protein, binds eIF4Erequired for assembly of pre-inc complex
What causes eIF2 release so 60S subunit can bind?
GTP hydrolysis
- only step that requires ATP
- once AUG found, eIF2 dissociates, eIF4E, eIF4G dissociate (stay at 5’ cap), ribosomal subunit binds
What is the movement of ribosome down mRNA and amino acid tRNA delivery called
Elongation
What is eEF1A
Binds all tRNAs except initiator and selenocysteine
- GTP bound to it
- delivery of aa-tRNA
How does eEF1A get released
GTP hydrolysis
-incorrectly base-paired tRNAs disassociates
What is eEF2
Catalyze so translocation; pushes from Asite to P site
- ribosome translocation
- proofreading in ribosomal A site codon/anticodon pair checked by ribosome conformation
What causes eEF2 release
GTP hydrolysis
-completion, A space is open for business
What is eRF1
Protein involved in termination
- swoops in and allows for peptide hydrolysis and termination
- recognizes any of the top codons
- there is no terminator tRNA; eRF1 catalyze a release of completed peptide
What dictates initiation in bacterial translation
Shine-dalgarno sequence
Is 5’ cap required in bacteria
No
Also transcription and translation is coupled
Describe bacterial ribosome
-smaller
70S ribosome (30S + 50S)
-allows for selective inhibition by ribosome inhibitor antibiotics
***has residual toxicity due to effects on mitochondrial ribosomes (more similar to bacterial ribosomes)
Counterpart of eIF4E in bacteria?
None, bacteria has no cap
Counterpart of eIF2 in bacteria
IF2
Counterpart of eIF4G in bacteria
None, initiation is fundamentally different
Counterpart of eEFIA in bacteria
EFTu
Counterpart of eEF2 in bacteria
EFG
What are micro RNAs (miRNAs)
Short RNA molecules that base pair with mRNAs and inhabit translation
Mechanism of miRNAs
-initiate form of RISC complex which impedes translation, initiation
-inhibits ribosome from getting any further, physical blockade of initiation complex
–>correlates with many diseases
3’ UTR: where regulation happens
Iron homeostasis regulated by ___
IRP in 5’ UTR
Low levels of iron >. IRP binds IRE > prevents translation of ferretin
- iron is a potent oxidant and need to bind it to ferretin
- if we have low levels of iron, don’t want to bind it to ferretin, production of ferretin tightly correlated with level of iron in cell
3 mechanisms of post transcriptional regulation of translation
1) mRNA editing
2) miRNAs
3) nutritional status
What happens to eIF2 when nutritionally deprived
EIF2 is phosphorylated & translation inhibited
We need eIF2B (a GEF that allows eIF2 to bind after hydrolysis)
-poor nutrition, eIF2 is phosphorylated & inactive eIF2B binds and no protein synthesis (non productive complex), reduces effective concentration of EF2B
If reducing concentration of eIF2B, there’s more eIF2 than eIF2B in cell
Why are GEFs required
Affinity for GDP»>GTP
G protein eIF2 needs GEF to re-assist in binding GTP after hydrolysis
What does mTOR path do in response to hypoxia and how
MTOR path represses translation in response to hypoxia via eIF4E (the 5’ cap binder)
~it up regulates translation during growth, down regulates during stress
During normoxia mTOR phosphorylated ____
4EBP-1
What does 4EBP-1 do
Binds eIF4E to inhibit translation
When it’s phosphorylated, can’t bind and translation proceeds
High mTOR activity in cancer, bc all 4EBP phosphorylated and translation rate very high
What happens during hypoxia
MTOR reduced, 4EBP-1 phosphorylation reduced, binds eIF4E and impedes translation
Selenocysteine is essential for
TH production, specifically devoid ashes
What is enzymatic ally converted t selenocysteine
Serine
-selenocystein has its own tRNA, uses a stop codon (UGA), it’s recoded to allow SEC-tRNA binding
What protein is necessary for recoding of stop codon to selenocystein
SBP2
Rare forms of hypothyroidism causes by
SBP2 mutation –>reduced Sec incorporation and decreased production of deiodinases
What is eEFSec
Specialized elongation factor, binds to Sec-tRNA
Similar to eEFIA
Sec-tRNA
Specialized tRNA, recognizes UGA codons, carries selenocystein amino acid
SECIS
RNA sequence in 3’ UTR
Required for Sec incorporation
SBP2 (SECIS. Binding protein 2) binds to SECIDS and assists in getting eEFSec tertiary complex to ribosome at UGA Sec codons
What is responsible for creating more than one protein from a single mRNA
Ribosomal frame shifting
-pseudo knot tells ribosome to stop & it goes back to slippery site
Frame shift signals: RNA pseudo knot & slippery site
Selenocystein encoded by ____ and has been re corded to allow Sec-tRNA binding, ____ is required for this recoding process
1) UGA stop codon
2) SBP2 protein
Pathogens is of C. Diphtheria with
Membrane receptor recognizes and binds toxin ->toxin enters via receptor mediated endophytes is -> toxin dissociates into 2 fragments -> fragment A translocation to cytosol & catalyes transfer of ADPR from NAD + to EF2 –> EF2 inactivated and peptide synthesis stops
How does diptheria toxin targets translation
Modifies elongation factor responsible to translocation
eEF2 (what pushes from A site to P site)
