FOM 5.4.2 Flashcards
What roles to the 5’ and 3’ UTRs have in translation?
These are sequences of the RNA that are not translated. They often contain conserved sequences that affect translation efficiency and mRNA stability
What are the key molecules in translational initiation?
Cap binding complex - recruits small subunit of ribosome to mRNA
Methionyl-tRNA - tRNA “charged with methionine
Ribosome - two subunits with protein and rRNA
Initiation factors - escort small subunit of ribosome to mRNA and escort met-tRNA to ribosome
What is the cap binding complex and what are the proteins that make it up?
eIF4F consists of eIF4A, G, and E
It ensures that only the mRNA is translated
It functions to recruit the ribosome and unwind secondary structure in mRNA
An the binding can be regulated to control translation
eIF4e is the limiting subunit!
What is the role of eIF4E?
limiting subunit it binds to the m7G-CAP
What is the role of eIF4G?
A scaffolding protein for the complex
What is the role of eIF4A?
it works as a helicase for the complex
What is the role of eIF4E in relation to come cancers and why would this occur?
Elevated eIF4E lead to increased transcription of weak mRNAs that would have otherwise been degraded. These weak mRNAs lead to proteins that had pro-cancer activities.
Why would there be increased translation of weak mRNAs in the presence of higher levels of CAP proteins?
The weak mRNAs would tend to be degraded otherwise, but with higher levels of CAP proteins (eIF4E) these mRNAs are translated.
What are the two subunits of the eukaryotic ribosome?
The eukaryotic ribosome is composed of the 60S subunit and the 40S subunit
What are the three sites of the ribosome and what is the role of each?
The A, P and E site
A - the aminoacyl site - aminoacyl-tRNA for next codon enters
P - the peptidyl site - site of growthing peptide chain attached to tRNA
E - empty site - tRNA moves from P site to E site
What does the tRNA rely on for chain elongation?
It relies of the condon-anticodon binding, and when there is a correct match the amino acid attached to the tRNA is added to the growing chain. The tRNA also contains intra-molecular basepairing.
What is the role of eIF2 in the initiation of translation?
eIF2 escorts methionyl-tRNA to the ribosome and once AUG is recognized eIF2 leaves and the large ribosomal subunit combines with the small subunit
What are the roles of eIF1 and 3?
These bind to the small ribosomal subunit and interact with the cap binding complex to bring the ribosome to mRNA
What are the initiation events that lead to translation?
- Cap complex (eIF4F) binds to mRNA cap
- eIF2 loads methionyl-tRNA onto small ribosomal subunit
- Small ribo subunit is recruited to mRNA
- Small subunit scans along mRNA
- Recognition of start codon and release of initiation factors
- Binding of large ribo subunit
The conserved sequence around a start codon is knows as?
Kozak sequence
What is the role of PABP in translational initiation?
PABP - poly A binding protein
This protein interacts with the polyA tail and cap binding complex leading to a drastically improved translation of mRNA
What is the protein that catalyzes the formation of peptide bonds?
Peptidyl transferase - peptide bond formation results in shift of nascent peptide from P-site to A-site
What is the role of EF2?
EF2 is the protein required for elongation of peptide and translocation of the ribosome
How does the diptheria toxin affect translation?
It blocks GTP hydrolysis of EF2 leading to shutting down of all translation
What is the role of EF1?
It escorts the next aa-tRNA to the vacant A site
What is the role of RF?
In protein translation termination, when the ribosome reaches a stop codon release factor (RF) binds to the A site. This catalyses the release of protein from tRNA and the disassembly of the ribosome.
What is a polysome?
It is when a single mRNA has many ribosomes located on it
In a situation of stress how is protein translation regulated?
Translation is shut down by the phosphorylation of eIF2. This is done by the PERK kinase, which is activated by in response to unfolded protein response. PERK then phosphorylates eIF2
Mutation in the PERK gene can lead to what?
The mutation in PERK gene leads to the protein having no/reduced kinase activity.
What could be the result of phosphorylating 4E-BPs?
It would facilitate the release of eIF4E which leads to increased translation
What is the role of miRNAs in regulation of protein translation?
These are nucleotide RNAs that regulate gene expression by repressing translation or destabilizing target RNAs
What is the difference between miRNAs and siRNAs?
miRNA - decrease translation
siRNAs - induce mRNA degradation
A patient has a myocardial infaction. What is the mechanism by which most protein translation is reduced in the affected cardiac myocytes?
Under stress the cellular integrated stress response is activated which leads to phosphorylation of eIF2, reducing its availability for translation
What is the initiation factor that “escorts” methionyl-tRNA to the small ribosomal subunit?
eIF2
Besides killing the bacteria what is the added benefit of inhibiting translation of an infectious disease have?
If the bacteria stops producing toxins, inhibiting translation stops their production even prior to killing the bacteria
micro-RNA has been highly expressed in many cancer types, in comparison to normal tissues. What might be the target mRNA of these micro-RNA?
Something along the lines of a tumor suppressor gene. miRNAs base pair with their mRNA and suppress the translation of mRNA.
