LEC26: Translation Machinery & Mechanism I Flashcards Preview

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Flashcards in LEC26: Translation Machinery & Mechanism I Deck (28):

what is translation?

what codes for what?

converting nucleic acid info into protein info

mRNA codon codes for nucleic acid


what is a tRNA?

what does it do?

transfer RNA 

recognizes an mRNA codon via its own complementary anticodon 

produces corresponding amino acid at its 3' end 


what holds together the tRNA structure?

intramolecular base pairing 


what is the structure of tRNA overall?

3' end CCA codon, A attaches via OH to alpha-carboxyl group of attached amino acid, covalent link

T loop, anticodon loop, D loop 

anticodon that's complementary to codon 

5' end 



do some amino acids have >1 tRNA to whicih they can be attached?



what do aminoacyl tRNA synthetases do?

covalently couple each amino acid to its appropriate set of tRNA molecules; diff synthetase enzyme for each a.a.


taks a.a. and activates teh a.a. 

must be able to discriminate vs. diff. a.a., which come into its active site 

thus has proofreading function so can recognize if it has put the wrong a.a. in place, so can go back, hydrolyze it off the tRNA


what is wobble pairing?

the last ntd in a codon and 1st ntd in anticodon don't have to be classic base pairing

not every codon requires a dedicated tRNA w/ standard codon:anticodon base pairing, can have variability in that position


what are the machines of translation?

mRNA, tRNA, ribosome


what do aminoacyl tRNA synthesases do?


catalyze covalent attachment of a cognate a.a., based mainly on anticodon sequence, to CCA 3' end of tRNA



attaches the amino acid to the 3' end of the tRNA 

an energy-releasing hydrolysis of ATP

produces high-energy bond btwn charged tRNA and the a.a. 

this bond's energy is used later in protein synthesis, links amino acid covalently to growing peptide chain


what is the structure of the ribosome?

what does each part do during translation?

large subunit = 60S; small subunit= 40S, together make 80S, contain proteins & rRNA 

small subunit: matches tRNAs to codons of mRNA 

large subunitcatalyzes formation of peptide bonds that covalently link a.a. together into polypeptide chain


what does rRNA do in the ribosome?

does catalytic fxn of ribosome - makes a peptide bond 

therefore ribosome is a ribozyme


what is the structure of the rRNA of the ribosome?

18S unit, 28S unit 



what is this? 


18S rRNA of the small (40S) subunit of the ribosome


what are the 3 "sites" on the ribosome for tRNA?

E=exit site; P=peptidyl site; A=aminoacyl site 

imagined sites where tRNA bond, do different stages of translation


which part of the tRNA binds to which part of the ribosome during translation?

bottom part of tRNA w/ anticodon is in 40S subunit of ribosome 

top part of tRNA w/ amino acid binds to 60S subunit of ribosome


what happens in each "tRNA site" on ribosome?

A site: wher enext charged tRNA binds 

P site: where tRNA w/ growing peptide chain is located 

E site: where tRNA in P site goes after its peptide cargo has engaged in peptide bond synthesis


what are eIFs? what do they do?


eukaryotic initiation factors 

bind ribsome to mRNA 5' end, position ribosome for correct translation initiation


what are eEFs? fxn?

eukaryotic elongation factors (have 3!)

bring succeeding charged tRNAs to the site on ribosome where peptide bond formation occurs 

also translocate ribosome to next codon


what is eRF? fxn?

eukaryotic release factor

just have 1!

relases finished polypeptide upon encountering stop codon, releases ribosome from the mRNA 


where does the first tRNA enter the ribosome? explain uniqueness of 1st tRNA

1st tRNA for AUG codon (Met) enters P site; every subsequent tRNA enters into A site

1st tRNA = tRNAi, initiation tRNA for Met 

have another tRNA for Met within the chain


what is the preinitiation complex of translation made of?

Met tRNAi in its GTP-bound state

also have 40S subunit, eIFs


ternary complex of Met-tRNAi-EIF2-GTP w/ 40S ribosome subunit, eIFs



what is the eIF4 complex of tln initiation factors?

form 5'-cap binding complex 

recognizes the cap specifically 

brings w/ it all the other eIF4s that make this complex of eIFS that're bound to mRNA


what does the 40S ribisome subunit do re: initiation of tln?

part of PIC 

binds the 5' end of the mRNA 

at expense of ATP hydrolysis, "scans" in 5' to 3' direction for an AUG that's in correct sequence context to fxn as start codon


what is the process of translation kozak scanning?

must find start codon, which is internal, after the 5'UTR 

find it by kozak scanning model: 40S of the PIC complex scans via ATP hydrolysis in 5' to 3' direction for an AUG start codon 


how does full ribosome get positioned for tln?

EIF2 departs from PIC, via hydrolysis of GTP to GDP

however, EIF2 isn't a good phosphatase; needs a GAP to work

EI5 is EIF2's GAP that hydrolyzes GTP to GDP 

NOW 60S subunit binds, 80S ribosome is formed


what happens to EIF2 after it's removed from PIC?

returns to its GTP-bound state via aid of GEF: eIF2B, which catalyzes exchange of GDP for GTP so now EIF2 can pick up next Met-tRNAi for next ronud of tln 


what is vanishing white matter disease?

an eIF2B defiency (the EIF2 GEF that restores GTP-bound state for EIF2) 

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