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Protein Synthesis P2
Protein Synthesis Part 2
Question | Answer |
---|---|
IF-3 | referred to as an anti-associtation factor. Binds to 30s |
IF-2, GTP & initiator tRNA | 30s initiation complex. Binding of mRNA |
In Pro what recognizes the shine delgarno sequence? | The 3' end of 16s rRNA recognizes the purine rich sequence. Then when 50s binds you get 70s complex |
What does f-Met-tRNA have to bind to in the ribosome? | The P site of the ribosome |
Name the steps of the elongation phase | Binding of amino-acyl tRNA, peptide bond formation, translocation, repeat of this process |
What does the binding of the 2nd aminoacyl tRNA sequence need for elongation? | Presentation of an elongation ternary complex. GTP required. Requires EF-TU (Pro) or EF-1alp (Euk). Binds to A site starting elongation process |
What happens after 2nd aminoacyl binds? | Peptide bond formation b/w 2nd and 1st aminoacyl tRNA located at P site. Outcome is dipeptide tRNA located at A site. P site is now free (deacylate tRNA) of AA |
Describe translocation | Requires EF-G & GTP. 1st aminoacyl tRNA gets ejected from P site to E site. Elongated peptide bond translocates from A site to P site. Ribosome is being moved in 5' to 3' direction cocurrently. |
How is the hydrolysis of GTP and EF used for delivering aminoacyl tRNA to A site presented? | Presented in the form as EF-TU together with the nucleotide GDP. GDP & GTP exchange is catalyzed by EF-TS |
What catalyzes peptide bond formation? | Ribozyme peptidyl transferase |
What does the termination step require? | GTP. Release causes the hydrolysis of peptidyl-tRNA so it can be released |
Describe Euk intiation complex formation | eIF-2 forms an initiation ternary complex which binds to 40s with eIF-3 to form a complex that binds with mRNA. Then 60s complex binds to form 80s initiation complex |
What 2 Euk initiation factors can limit the formation of the 80s initiation complex? | eIF-2 and eIF-4. eIF-2-GDP has to be regenerated to eIF-2-GTP by eIF-2B |
Describe Euk mRNA | m7G is recognized by eIF-4E. 5'UTR recognizes the first initiation. Many viral mRNA and 10% of mRNA have IRES and no cap |
beta and alpha globin | beta globin is a much better recruiter of mRNA relative to alpha globin. beta globin has a secondary structure that is more favorable to being unwound |
IRES mRNA's | long 5' UTR 400-500nts. Can have secondary structures very high in G & C content.Usually encode for proteins with specialized functions |
What does virally encoded protease do? | Degrades eIF-4G. host mRNA is no longer translated in a very efficient way b/c it has a truncated eIF-4G that lacks the ability to recognize eIF-4E |
Translational Control | Ability to modulate the tranlability of the mRNA in the absence of any transcriptional input. There is no change in mRNA content/no trascriptional input. |
Describe the alternate pathway for eIF-2-GDP (Translational Control) | Kinase mediated phosphorylation at alpha subunit at serine, eIF-2 continues to bind with eIF-2B and sythesis is at standstill |
Describe alternative pathway for eIF-4 (translational control) | Binds to eIF-4E binding protein. Brings eIF -4E into a form that is incapable in being engaged in mRNA binding |
How does insulin play a role in eIF-4E? | Brings about a set of kinases that can phosphorylate eIF-4E 7 its binding protein so it can no longer associate with eIF-4D as normal to bind mRNA |
Signal peptide | Sequence of AA residues that is highly enriched in hydrophobic amino acid residues. |
How is signal peptide sythesized? | Ribosome is cytosol & protein is tagged. SRP binds and stalls synthesis. SRP has to dock a docking protein or SRP receptor. GTP hydrolyzed and SRP released. |
Name inhibition drugs | Cyclohexamide of Euk inhibits peptidyl transferase. Puromycin of Euk and Pro resembles charged tRNA , binds to A site and terminates process |
Ricin | Ribosome inactivating protein. Catalyzes depurination of rRNA at 28S rRNA. Formation of an Abasic site at the RNA level, not DNA level |