6. Translation Flashcards
start codon
AUG (met)
codons
3 nucleotides long
each codon represents one AA
(AAs can be represented by many codons)
stop codon
UGA
UAG
UAA
direction code is being read for translation?
5’ to 3’
tRNA
used to read the codons on the mRNA
uses anticodon to base pair with a codon on mRNA
5’ position of the tRNA on the anticodon
wobble position
inosine
modified base (I)
created by deamination of guanine
when present in the wobble position of the anticodon, can recognize:
U or C in euks
U, C, or A of proks
aminoacyl-tRNA synthetase
activates an AA for protein synthesis in 2 steps
- uses ATP to adenylate the AA
- creates an amino-acyl tRNA
AA is now linked to tRNA via carboxy, makes HIGH ENERGY ester linkage
once tRNA is activated w/AA?
can bind to mRNA complement
hydrolytic editing
if wrong AA is added to tRNA, they will bind incorrectly to the synthetase and then bind the editing site
in the editing site, the incorrect AA will be removed an the correct one added
translation occurs? (what direction)
N to C terminus
bacterial v. eukaryotic ribosomes
bacterial: 50s, 30s, 70s
eukaryotic: 60s, 40s, 80s
each ribosome contains?
binding site for mRNA
3 for tRNA: A site (aminoacyl-tRNA), P site (peptidyl RNA), E site (exit)
elongation step 1
aminoacyl-tRNA binds A site
used up RNA leaves through E site
elongation step 2
new peptide bond formed (peptidyl transferase activity)
elongation step 3
large subunit translocates relative to small subunit–leaving 2 tRNAs in hybrid site; P site & E/P site
elongation step 4
small subunit translocates a distance of 3 nucleotides to catch up with the large subunit, carrying mRNA with it
ribosome now has an empty A site (ready to bind another aminoacyl-tRNA)
elongation factors
EF1=EF-tu
EF2=EFG
what do elongation factors do?
provide free energy to drive rxn fwd
use GTP hydrolysis as signal
EF1
bound to GTP, helps delive an actiated tRNA to an empty A site
proofreading pause to ensure that the anticodon match is correct
if correct match
GTP is hydrolyzed, tRNA is delivered
if incorrect match
no GTP hydrolysis
elongation cannot continue until there is a proper match
16S RNA of the small ribosomal subunit
helps recognize proper binding between the codon and anti-codon
forms an H bond network with the first nucleotide or a correct codon-anticodon pairing
after you get proper binding?
EF2 bound to GTP binds to ribosome causing the large ribosomal subunit to ratchet forward
hydrolysis of GTP causes the small ribosomal subunit to follow, freeing up the A site
initiation: eIF2
GTP bound protein that uses GTP hydrolysis
helps chaperone the tRNA to bind the small ribosomal subunit–>binds 5’ cap of mRNA to be translated–>initiator tRNA will then scan 5’ to 3’ looking for Met in appropriate context
once the consensus recognition sequence encountered?
hydrolysis of GTP on eIF2
removal of eIF2
recruitment of large ribosomal subunit
elongation can now begin
termination
stop codon enters A site, releasing factor protein mimics the function of a tRNA and binds to the codon, triggering termination
example of molecular mimicry?
releasing factor protein
mimics shape and function of tRNA, but serves to terminate translation
polyribosomes
many ribosomes working together on the same mRNA molecule to synthesize proteins
final protein production depends on efficiency of what?
- initiation of transcription
- generation of primary transcript
- generation of mRNA that can get transported into cytoplasm for translation
points of regulation of translation (4)
- binding of small molecule to part of mRNA secondary structure (riboswitch), induces autolytic ribozyme activity
- riboswitch causes structural rearrangment of RNA, blocking translation initiation
- thermosensor: increased temp can alter the structure of some pathogenic RNA by melting AT rich regions; allows for translation of pathogenic proteins
- antisense RNA: can basepair with a specific mRNA, blocking the start codon and thus translation
