Protein translation and post-translational modification Flashcards
explain why some antibiotics inhibit protein synthesis in prokaryotes but not eukaryotes
70s ribosomes - prokaryote 80s ribosomes - eukaryote have different RNA and proteins antibiotic selectivity inhibits AA natural products of bacteria/fungi - give them a selective advantage
features of proteins that allow them to enter the secretory pathway
signal sequence - hydrophobic AA sequence recognition halt translation until bound to RER grow into lumen cleavage by signal peptidase co-translational - as soon as translated it is about to be cleaved
summarise the ways in which newly-synthesised proteins can be post-translationally modified
phosphorylation proteolytic cleavage - insulin A--B (secretory vesicle) lipid groups - phenylation/acylation hydroxylation - collagen disulphide bond formation (insulin) addition of carb (glycosylation) addition of phosphate (phosphorylation)
describe the 40s subunit of ribosomes
the rna folds in on itself
What is the direction of protein translation
mRNA transcribed in 5’-3’
N-C terminus
describe the structure of mRNA
5’ cap - 7-methyl guanosine - entry site for ribosome
poly-A - protect from degradation
UTR (untranslated regions) involved in regulation of translation/stability
how many codons are there
64
common AA several codons
because widely used
describe the reading of mRNA
ribosome scans from 5’ of mRNA
translations starts at AUG
continues in frame
stops at first in frame stop codon
describe tRNA
transporters of AA to ribosome single strand fold in tertiary structure anticodon exposed antiparallel binding
describe the function of aminoacyl tRNA synthetases
1 for each AA important in fidelity of translation - selectivity for correct AA and tRNA, hydrolysis of incorrect aa-tRNA help tRNA hook AA to tRNA AA -- E-AMP-AA complex come to specific tRNA - recognition step remove AMP and enzyme hooked to side at 3' ready to go to ribosomes
describe initiation of translation
- dissociation of ribosome subunits
- assembly of pre-initiation complex - e1F4E and e1F4G bind to cap and are recognised by 40s/Met-tRNA/eIF2
- binding of mRNA to pre-initiation complex - Met binding sets frame of translation
- binding of 60s subunit - GTP-GDP + Pi - ensure binding to correct base pair
describe elongation of translation
factors movement of ribosome using GDP
- bind tRNA in A site on ribosome in frame with met
- peptidyl transferase catalyses peptide bond between 2 AA
- Translocation of peptidal tRNA to P site - elongation factors promote movement with GTP
- new cycle
- EFs - GTP hydrolysis provide pauses to increase accuracy of translation
describe termination of translation
- recognise stop codon - hydrolysis (peptidyl transferase) - release factors bind to empty A site
streptomycin
inhibit initiation
tetracycline
inhibit aa-tRNA binding
