Lecture 6 Flashcards
(41 cards)
How many reading frames are in dsDNA and mRNA?
6 dsDNA
3 mRNA
Open reading frame contains?
1) start codon
2) coding sequence
3) stop codon
Eukaryotic tRNA molecules transcribed by?
RNA pol. III
Eukaryotic tRNA molecules are processed….?
before leaving nucleus, trimed, and spliced (catalyzed by proteins)
What % of tRNA are modified bases?
10
Modified bases of tRNA molecules influence?
mol. conformation, base-pairing, amino acid coupling
Degenerate genetic code (numbers only)
4^3= 64 codons code for 20 amino acids
What are 2 possibilities that allows genetic code to be degenerate?
1) multiple tRNAs with multiple anticodons
2) 1 tRNA (with one anticodon) can regonize multiple codons
aminoacyl-tRNA synthetase
is a dual check mechanism that couples correct amino acid to cognate tRNA, where tRNA acts like activated carrier to shuttle activated amino acid
How does aminoacyl-tRNA synthetase assure correct amino acid pairing?
synthetase assesses nucleotide sequences of 1) anticodon, 2) amino acid acceptor arm, and 3) several other positions of tRNA
Where does translation occur?
ribosomes in the cytosol (E, P, A site)
Translation mechanism
1) small and large ribosomal subunits assembled at nucleolus
2) binding of mRNA joins subunits together to fomr a ribosome
Large ribosome subunit contains what?
peptidyl transferase activity
Peptidyl transferase activity mechanism
peptidyl-tRNA ttached to CTD of growing polypetide chaine
aminoacyl-tRNA frees tRNA molecules from peptidyl linkage
new peptidyl-tRNA molecule attached to CTD of growing polypetide chain
3 tRNA binding sites are?
Aminoacyl-tRNA
peptidyl-tRNA
Exit
How many tRNA binding sites are occupied at the same time?
2
EF-Tu proofreading mechanisms for improving translation fidelity?
1) tight codon-anticodon pairing
2) delay of peptidyl-residue transfer
Ef-Tu: tight codon-anticodon pairing
16S rRNA triggers conformational change in ribosome, EF-TU catalyzes GTP hydrolysis and dissociates from amino acyl group of tRNA
eF-tu: peptidyl-residue transfer delay
weakly bound tRNA in A site, will cause tRNA to dissociate before peptidyl residue can be transferred
EF-G
move ribosome forward
How do biological processes overcome limitations to complementary base-pairing?
induced fit, kinetic proofreading and the sequential se of both mechanisms
Why is translation initiation important?
determines reading frame and translation frequency
Translation initiation mechanism
1) MtRNA + eIFs bind to small rSU in P site
2) Small rSU binds to 5’ cap with bound eIF4 E + G
3) Small rSU searches for first (5’ located) AUG eIFs drives this movement via ATP hydrolysis)
4) Encounter of start codon releases eIFs and
large rSU binds
Bacterial translation initiation is mediated by?
Shine-Dalgarno sequence (AGGAGGU)