BC 17 Translation Flashcards
Translation
Makes it 5’-3’
5-NH2 3-COOH
most higly conseved process
most energetically costly
mRNA
tRNA
aminoacyl tRAN syntesis
ribosomes
START and STOP
Start: AUG methionine
-begins translation and DEFINES FRAME
STOP: UGA, UAG, UAA
Mutations
Missense: mutation that results in different amino acid
Nonsense: STOP CODON
Silent: same AA
Frameshift: can be missense or nonsense
degenerate
genetic code description
all AA are made by at least TWO codonds (triple letters)
tRNA
transfer
75-90 nucleiotides in length
-cloverleaf, self complementary
(3D L with four relevant sites)
- 3’ CCA-OH for attachment
- AA attache to ribose adenine (of CCA) - anticodon triplet sequence that is used to base pair to one or moe codonds for an AA in an antiparallel fashion
CODONS written in 5-3 direction whereas anticodons in tRNA are written in 3-5 direction
-anticodon for methionine UAC-5’
aminoacyl tRNA synthetase
determines accurace of protein syntehsis
- adds correct addition of AA to its appropriate tRNA
- different aa-tRNA synthetase for each AA
-proper H bonding between mRNA and anticodon of tRNA also makes difference.
basically brings AA and tRNA with corresponding sequence together, linkage is ATP dependent. (HIGH ENERGY BOND)
bound tRNA to mRNA is CHARGED
Ribosomes
protien synthesis
multisubunit
- large-catalyze peptide bond formation
- small- decoding center: binds to the mRNA and the tRNA
-one mRNA can have multiple Ribosomes bound for more production
A; Aminoacylated tRNA site
P: peptidyl tRNA site
E: exit site
A: aminoacylated tRNA site
Incoming site, incoming CHARGED tRNA dock here according to mRNA sequence when ribosome bound,
the PP chain bound to a tRHA at teh P site forms a covalent bond with the AA at teh E site, then moves from E to P
peptidyl site (Psite)
once the peptide bond has formed at teh A site, the tRNA with newly elongated chain moves here. No peptide bonds are fomed here.
E site
Exit site, release tRNA with no pp chain
Translation Factors
IF - eIF2
EF - eIF4E, eIF4G
RF - eF1alpha
prokaryotic translation
multicistronic
euk, mono
Prokaryotic translation factors
Shine Delgarno Sequence
-ribosomal binding site (16s rRNA aka SMALL), just upstream, aligns with start codon
-binds ribosomes to every start site between cistons
Eukaryotic ribosome binding site
5’ cap recruits small ribosomal subunit. Ribosome SCANS 5-3 looking for AUG
also, ????
initiatior tRNA binding to a conserved sequence
polyA tail (for recycling of ribosomes)
eIF4G eIF4E
bind to 5’ cap and position RNA on small ribosomal subunit. (uncoupled transcription/translation)
mainly transport
eukaryotic translation initiation
- charged initiator tRNA binding to eIF2. which is bound to GTP
- Binding of eIF2/GTP to the tRNA brings the tRNA to the small ribosomal sununit.
- eIF4G and 4E bind to the 5’ end of the mRNA
- small ribosomal subunit the binds to 5’ end of mRNA
- small Rb subunit scans for first AUG
- Once the correct AUG is located GTP is hdrolized. eIF2/GDP dissociates and large subunit joins
- eIF2 releases GDP and bind new GTP before it can initiate again
- met-tRNA must be at P site for initiation
Euk Elongation
- correct AA tRNA into A site,
- peptide bond between aaTRNA in A and aa tRNA in P (peptidul transferase)
- aa tRNA in A site translocates to P site, (EF’s and GTP hydrolysis)
- aatRNA do not bind to ribosomes on their own, must be escorted by EF1alph and GTP
- EF1alpha binding prevents peptide bond formation until EF1alpha releases tRNA-hydrolysis
- hydolysis, ef1alpha leaves
- peptidyl tranferase catalyses bond formation.
- release also initiates move to E site
euk termination
UAA UAG UGA
no rRNA with anticodon complimentary to termination codon
instead relast factors eRF;s that recognize termination codons and terminate
Bind at A site and stimulate hydrolysis of pbond between tRNA and pp chain at P site. Release PP chain.
tRNA then relased, and RIb and mRNA dissociate
streptomycin
affects innitiation
inhibits, causes misreading
tetracycline
ihibits elongation byu hinding of aminoacyl tRNA from binding site to A site
chloramphenicol
inhibits elongation byt targeting peptidyl transferase center, blocks positioning of A site
Erythromycin
ihhibits elongation. prevents translocation from a to p
