Protein Translation Flashcards
What are 6 features of mRNA. Draw it out in your mind.
- 5’ cap
- 5’ UTR
- AUG start codon
(open reading frames) - stop codon (UGA, UAA, UAG)
- 3’ UTR
- 3’ end poly a tail
Draw a tRNA molecule in your mind.
ok
How many bases make up a codon?
3
How many possible codon sequences are there?
64
What is inosine?
found in tRNA and can pair with A, C, or U
aminoacyl-tRNA synthesis?
tRNA + aminoacid + ATP = aminoacyl-tRNA + ADP + P
In what part of the cell does translation occur?
cytosol
Where do ribosomal subunits come from?
rRNA genes transcribed and processed in the nucleolus
After ribosomal subunits are synthesized in the cytosol, where do they go?
imported into the nucleus
Initiation of translation requires the correct assembly of what 3 things?
- small ribo subunit
- mRNA
- tRNA binds to the first codon, usually a methionine-tRNA met pairing with the AUG start codon
What are the 5 initiation steps of translation?
- eIF2a is activated by binding GTP
- binds initiator methionine-tRNA met to form the ternary complex
- binds small ribo subunit
- mRNA molecule binds –> pre-initiation complex
- large rib subunit binds –> initiation complex and eIF2a is hydrolyzed and released
What are the 5 steps of elongation?
- initiator methionine-tRNA binds to the P site of the ribosome
- a second aminoacyl-tRNA is placed into A site; requires EF-1/GTP
- peptidyl bond is formed between first and second AA
- ribosomes moves down one codon; assisted by EF-2;
- the mRNA-peptidyl-complex now occupies the P site and the A site is empty; uncharged tRNA leaves throuhg E site
Describe termination?
- stop codon enters A site
- eRF pairs with the stop codon
- erF-GTP is hydrolyzed and peptide is released from P site
What is eRF?
it binds to the stop codon with GTP and assisted the releasing of the peptide
What 4 types of antibiotics inhibit the growth of prokaryotes by selectively inhibiting prokaryotic ribosomes
- Streptomycin: binds to the small subunit and inhibits initiation
- Neomycin/Gentamicin: binds to ribosomes and causes mistranslation
- tetracyclin: blocks the A site and prevents tRNA form binding
- Chloramphenicol: prevents peptidyl bond formation
What are 2 ways to regulate translation?
- regulation by preventing the recognition of a start codon
2. regulating the activity of initiation factors
How is ef-2 inhibited (in general terms.. nothing specific)
phosphorylation
Secretion of protein steps (4)
- signal sequence emerges and SRP binds the signal and complex moves to ER
- SRP docking protein transfers the ribosome to the translocon
- SRP dissociates and translation continues and peptide is threaded into the ER
- signal peptidase cleaves the signal peptide
What is the unfolded protein response?
- decrease in translation
- increase in chaperone proteins
- apoptosis
Why is glycosylation important (2 reasons)
- changes the physical properties of the protein by increasing solubility, stability, and size
- carbs prob recognition sites (important for development or immune defense)
Where does glycosylation of proteins begin? Where does it continue?
In the ER.. then in the mitochondria
The unfolded protein response occurs in response to what 2 things?
starvation and cholesterol overload
What are the steps of N-linked glycosylation?
- 2 GlcNACs from UDP-GlcNAc –> Dolichol P
- a mannosyltransferase transfers a mannose from UDP-mannose to the 2 GlcNAcs (7 sugars now)
- reorientation of the oligosaccaride into the lumen
- more mannoses from dolicholphosphomannose; glucose from dolicophosphoglucose
- we now have the core structure: 2 GlnNAcs linked to mannoses which are linked to 3 glucoses
- ribosome attaches to translocon and peptide chain grows
- core is transferred to an aspargine residue in the nascent polypetide chain
What is the core structure considered to be in N-linked glycosylation?
dol phos + 2 GlcNacs linked to mannoses which are linked to 3 glucoses
