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?
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
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
READ tRNA SYNTHETASE-catalyzed RXN
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 subunit: catalyzes 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)