3.12 Translation Flashcards
Central dogma
DNA to RNA to protein
Genetic code is __. Why?
degenerate
More than 1 codon for many AA
Wobble base is what position?
3rd
What are the “non-sense codons”?
UAA
UAG
UGA
Start codon for bacteria and eukaryotes
Bacteria = FMet
Eukaryotes = Met
Define wobble base rule
a tRNA that recognizes a Pu at the 3rd position of the codon can recognizes the other Pu and vice versa w/ Py
Inosine (hypoxanthine + ribose) can pair with what bases?
A, C or U
5 overview steps for translation
- Charging of tRNA with AA by tRNA synthetases
- Initiation
- Elongation
- Termination
- Post-translational processing
The charging of tRNA to have AA attached to it is done by what enzyme?
tRNA synthetase
How many ATP are used to charge tRNA?
2
What site does charged initiator tRNA go to?
P site
(all others enter A site)
Do bacteria or eukaryotes have a ribosome binding site?
Bacterial (shine-dalgarno sequence)
What are the ribosome positioning mechanisms for eukaryotes?
Cap-dependent and cap-independent
What are the bacterial ribosome subunits?
30S + 50S = 70S
What are the eukaryotic ribosomal subunits?
40S + 60S = 80S
What are the 3 sites on the ribosome and describe?
A = tRNA binding site and accepts charged tRNA
P = contains previous tRNA attached to the growing polypeptide
E = exit for uncharged tRNA
Elongation of AA in bacteria is catalyzed by formation of peptide bonds by ___ rRNA
23S
Where is the shine-dalgarno sequence located in bacteria?
5-10 nucleotides upstream of FMet (AUG)
What IF binds to mRNA to position the ribosome in the correct place in bacteria?
IF-1 and IF-3
What helps bind tRNA FMet to the P site in bacteria?
IF-2:GTP
When does the 50S ribosome bind to 30S in bacteria?
With the removal of IF-1 and IF-2 and hydrolysis of GTP to GDP
Bacteria initiation steps:
- IF-1 and IF-3 bind to 30S subunit
- IF-2:GTP recognizes tRNA with F-Met and helps it bind to P site
- Triggers release of IF-3
- IF-1, IF-2, and GDP are ejected
- 50S subunit comes in = 70S subunit formed
Bacteria elongation steps
- EF-G with GTP enters ribosome and catalyzes ribosome translocation
- EF-Tu + GTP brings in charged tRNA to A site
- Hydrolysis of GTP kicks EF-Tu + GTP +Pi out of ribosome
- EF-Tu is recycled, so GDP is displaced by EF-Ts to form EF-Tu/EF-Ts complex → EF-Ts is replaced with GTP → EF-Tu + GTP to bring in another charged tRNA
A to P to E site - Peptide bond forms formed between AA (at carboxyl group) on P site and AA in A site
- Translocation of growing peptide chain onto A site
Termination in bacteria:
- Uncharged tRNA causes RF-1 (UAA and UAG) or RF-2 (UAA or UGA) to come in
- Ribosome release factor (RRF) and EF-G:GTP cause 70S dissociation
Define polysomes
Complex of several ribosomes attached to mRNA
- In bacteria
2 reasons why transcription and translation occur simultaneously in bacteria
- Increases rate of protein synthesis
- protect mRNA from nucleases
Why are there pausing sites in transcription in bacteria?
RNAP moves faster than ribosomes, so by having RNAP pause it allows the ribosomes to catch up
Is there a ribosome binding site in eukaryotes?
No
rRNA and ribosomal proteins are assembled in the
Nucleus
Where are the ribosomal subunits assembled in eukaryotes?
in the cytosol
What does translation need in eukaryotes?
5’-cap, 3’ poly A tail, and initiation factors
What scans mRNA until it reaches AUG?
43S preinitiation complex
What is the 43S preinitiation complex made of?
40S ribosome, eIF2-GTP, and tRNA Met
When does the large ribosomal subunit bind in eukaryotes?
Once 40S subunit reaches the start codon
Steps for initiation in eukaryotes:
- Formation of 43S preinitiation complex
- It then binds to 5’ cap
- PABP binds to poly A tail
- Initiation complex scans until it reaches AUG
- 60S joins to form 80S ribosome
Steps for elongation in eukaryotes:
- EF-1A + GTP brings in charged tRNA to A site
- Hydrolysis of GTP kicks EF-1A + GTP out of ribosome
- EF-1A is recycled, so GDP is displaced by EF-1Balpha to form EF-1A/EF-1Balpha complex → EF-1B is replaced with GTP → EF-1A + GTP to bring in another charged tRNA
Steps for termination in eukaryotes:
- Uncharged tRNA causes RF-1 (UAA and UAG) or RF-2 (UAA or UGA) to come in
- RF-3 aids in the activities of RF-1 and RF-2
- Ribosome release factor (RRF) and EF-2:GTP cause 80S dissociation
What are the post-translational modifications?
- Removal of Fmet or Met
- processing
- modification
- chelation (metals)
Why is enzyme degradation important?
Limits the activity and is a regulatory control
Most proteins in bacteria degrade by
AAA+ ATPases
Most eukaryotes degrade by
ATP-dependent
Lysosomal protein turnover
Why would proteins be degraded?
If they’re defective or damaged they AA are recycled to prevent mishaps
