Translation Flashcards
What are the steps before translation? Where do they happen? Where does translation happen?
Translation is the final part of gene expression. Transcription, capping, splicing and polyA need to be done before. These happen in the nucleus, while translation happens in the cytosol/ER
What is the RNA trio for translation?
messenger RNA, transfer RNA and ribosomal RNA
How many codons are there? For how many aa? which ones are special? When does translation start and end?
64 codons for 20aa. 3 stop codons -UAA, UAG and UGA
Translation always scans from capm and starts at AUG methionine codon and goes until a stop codon is reached
What is the structure of ribosomes? Are they the same everywhere?
2 main subunits-large and small. always composed of many proteins and rRNA combines. Smaller one binds cap and scan RNA, larger ones incorporates tRNA.
Prokaryotes have a 70S ribo (50S+30S) and eukaryotes have 80S (60S+40S)
Describe tRNA in regards of their structure, role and synthesis
Often represented by 3 leaf clover-with a loop with anti-codon (complementary of codon). 3’ end carries the aa, bound by AMP. Only one aa per tRNA/Codon, but more than 1 codon/tRNA per aa.
Synthesised by condensation with aminoacyl tRNA transferase-one per tRNA (highly specific)
Describe the 4 steps of initiaion
1: dissociation of Ribosome. elF4E/G bind cap-recognised by tRNAmet, eLF-2(GTP), 40S -pre-initiation complex binds mRNA. Scans and 60S subunit with hydrolysis of GTP-release ELF2GDP
Describe 3 steps of elongation
Met is in P site-2nd aa binds in A site. 60S peptyl transferase then puts the met on the 2nd aa (uses GTP), and move it all to P site and release met-repeat for each aa
Describe termination
Once stop codon is recognised, protein release factor is added to A site-cant transfer peptide to. Peptyl transferase catalyses it to water, releasing the chain-released with COOH on C end -then all the factors/ribo/mRNA dissociate and are released
What are polyribosomes?
More than one Ribosomes works on an mRNA at one time-multiple proteins made at the same time, as soon as the cap is free-like string of beads.
What is the relation between Abx and Ribsomes?
Because prokaryote have different ribsomes-tagretted
Ribsome are complex and therefore easily disrupted, so Abx exploit the differences
eg: streptomycin inhibits initiation
Tertracyclin inhibits aa-tRNA binding
Were are secretory and TM proteins synthesised? What happens to them?
start in cystosol, but as localisation sequence comes out, pushed into RER. Signal sequence bound and recognised by SRP, and brought to SRP receptor. Peptide is pushed through membrane of ER through a pore
Finally signal sequence is cleaved and protein folds. Then post translational modifications.
Describe post translation modifications and give an exemple
Post translational modifications happen after synthesis in the ER or golgi-adding disulphide bonds, cleavage, glycosylation, phosphorylation, hydroxylation, etc
Insulin for exemples is synthesised as a long chain-3SS bonds aded then large part cleaved
