lecture 7 - translation Flashcards
who figured out translation/what all the AA were
nirenberg, matthaei, gobind khorana, ochoa
what is AUG
methionine (and start)
what are the stop codons
UAA, UAG, UGA
explain structure of tRNA molecule
74-95 bases that fold into cloverleaf secondary structure with 4 constant arms and addition arm in loner tRNAs
has acceptor stem, TYC loop, variable loop, d loop
has anticodon sequence that is complementary to codon sequence on mRNA
the 3’ end is longer than 5’ end
how do tRNAs form aminoacyl-tRNA
ester link from 2’ or 3’ OH group of A base at 3’ end of acceptor arm to COOh group of AA
how is the specificity of aminoacyl-tRNA determined
sequence of anticodon
how many aminoacyl-tRNA enyzmes are there
one for every AA
what is the wobble hypothesis
if the base is in the third position of the codon then it can pair with more things (don’t need a separate tRNA for each of the 61 codons)
what are ribosomes characterized by
their rate of sedimentation
what are the rate of sedimentation for bacterial and euk ribosomes
bac –> 70S
euk –> 80S
how many subunits in ribosomes and what are there sizes for bac and euk
2 (large and small)
bac: large –> 50S, small –> 30S
euk: large –> 60S, small –> 40S
what are the rRNA sizes for bac and euk ribosomes
bac: large –> 23S & 5S, small –> 16S
euk: large –> 28S & 5S, small –> 18S
explain translation initiation in prokaryotes
- Initiation Factors (IF) 1 and 3 cause large and small subunits to dissociate so the small subunit binds to mRNA (binding helped by 16S RNA and Shine-Dalgarno sequence) IF1 and IF3 bind to 30S unit
- IF2 brings initiator tRNA to the start codon and the tRnA binds to the start codon (with met obvi)
- the large subunit reattaches with the tRNA in the P site (this is the only time that the tRNA ever enters in the P site instead of the A site
what are the 3 sites of the large ribosome subunit
exit, peptidyl, aminoacyl (E, P, A)
explain elongation for translation
- elongation factor (EF) Tu*GTP binds to aminoacyl-tRNA and place it in A site (AA for next codon)
- hydrolysis of GTP releases EF-Tu after aminoacyl-tRNA pairs with codon
- peptide bond is formed between the growing chain and the next AA (that is currently in the A site) which is catalyzed by 23S rRNA
- uncharged tRNA moves from P to E site and is released
- peptide chain moves down from A to P site
