lecture 7 - translation

Question 1

who figured out translation/what all the AA were

Answer 1

nirenberg, matthaei, gobind khorana, ochoa

Question 2

what is AUG

Answer 2

methionine (and start)

Question 3

what are the stop codons

Answer 3

UAA, UAG, UGA

Question 4

explain structure of tRNA molecule

Answer 4

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

Question 5

how do tRNAs form aminoacyl-tRNA

Answer 5

ester link from 2’ or 3’ OH group of A base at 3’ end of acceptor arm to COOh group of AA

Question 6

how is the specificity of aminoacyl-tRNA determined

Answer 6

sequence of anticodon

Question 7

how many aminoacyl-tRNA enyzmes are there

Answer 7

one for every AA

Question 8

what is the wobble hypothesis

Answer 8

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)

Question 9

what are ribosomes characterized by

Answer 9

their rate of sedimentation

Question 10

what are the rate of sedimentation for bacterial and euk ribosomes

Answer 10

bac –> 70S
euk –> 80S

Question 11

how many subunits in ribosomes and what are there sizes for bac and euk

Answer 11

2 (large and small)
bac: large –> 50S, small –> 30S
euk: large –> 60S, small –> 40S

Question 12

what are the rRNA sizes for bac and euk ribosomes

Answer 12

bac: large –> 23S & 5S, small –> 16S
euk: large –> 28S & 5S, small –> 18S

Question 13

explain translation initiation in prokaryotes

Answer 13

1. 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
2. IF2 brings initiator tRNA to the start codon and the tRnA binds to the start codon (with met obvi)
3. 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

Question 14

what are the 3 sites of the large ribosome subunit

Answer 14

exit, peptidyl, aminoacyl (E, P, A)

Question 15

explain elongation for translation

Answer 15

1. elongation factor (EF) Tu*GTP binds to aminoacyl-tRNA and place it in A site (AA for next codon)
2. hydrolysis of GTP releases EF-Tu after aminoacyl-tRNA pairs with codon
3. 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
4. uncharged tRNA moves from P to E site and is released
5. peptide chain moves down from A to P site

Question 16

explain termination in translation

Answer 16

1. stop codon is recognized by release factors (RF1 or RF2) and the binding is aided by RF3
2. peptide is transferred to water molecule
3. ribosome dissociates