Lecture 10

Question 1

translation

Answer 1

joining of aminoacyl residues by the ribosome to form a polypeptide

Question 2

which antibiotic inhibits the peptidyl transferase in the ribosome

Answer 2

erythromycin

chloramphenicol

Question 3

what retains peptidyl trnasferase activity

Answer 3

naked 23s rRNA

Question 4

colicin E3

Answer 4

a protein that inhibits growth of bacterial cells that lack the Col plasmid.
cleaves 16s rRNA 50 nts from its 3’ end. The cleaved fragment has 6 nts complementary to the ribosome binding site of the mRNA so ribosomes cannot initiate protein synthesis

Question 5

where is the P site located

Answer 5

50S subunit

Question 6

where is the E site located

Answer 6

50S subunit

Question 7

5 unusual the tRNA may contain

Answer 7

dihydrouridine
pseudouridine
inosine 
N-methylguanosine 
ribothymidine

Question 8

what are shared reactions of tRNAs (4)

Answer 8

interaction with EF except initiator tRNA
binding to ribosome A site
CCA terminal addition
invariant modifications to bases

Question 9

Unique reactions of individual tRNAs

Answer 9

amino acylation by synthetases
codon-anticodon interaction
recognition of initiator of initiator by initiation factor
recognition of initiator by transformylase

Question 10

identity elements

Answer 10

features of individual tRNAs recognised by their cognate synthetase

Question 11

at which stages does proofreading occur by aminoacyl-tRNA synthetases

Answer 11

• hydrolysis of the ester bond of an incorrect aa-AMP intermediate triggered by binding of the cognate tRNA
• hydrolysis of the ester bond of a mismatched aa-tRNA

Question 12

how does aa-tRNA editing?

Answer 12

flexible CCA arm can move aa between activation and editing site. if it fits well into the editing site it is removed by hydrolysis

Question 13

streptomycin

Answer 13

highly basic trisaccharide

binds 16s rRNA of 30S and thereby prevents the correct initiation of protein synthesis

Question 14

puromycin

Answer 14

resembles aa part of aa-tRNA
substrate for peptidyl transferase through its amino group forming peptidyl puromycin
peptidyl puromyci not anchored to the A site and dissociates from the ribosome resulting in premature chain termination

Question 15

how does diptheria toxin affect translation

Answer 15

produced by pathogenic strains of corynebacterium diptheriae. acts catalytically on EF-2 (homolog of EF-G). all EF-2s contaain a post translationally modified histidine residue called dipthamide. The toxin transfers ADP ribose from NAD+ to the imidazole ring. This completely inhibits translation.