B2.053 Prework 1 Protein Translation

Question 1

where do translation initiating complexes assemble?

Answer 1

7-methyl guanosine cap of mRNA

Question 2

what is the function of the cap binding complex?

Answer 2

recruits small subunit of ribosome to mRNA

adaptor between the cap and ribosome

Question 3

what is the name of the cap binding complex?

Answer 3

eIF4F

Question 4

what 3 subunits make up eIF4F?

Answer 4

eIF4A eIF4G eIF4E

Question 5

which subunit of the cap binding complex is limiting?

Answer 5

eIF4E

Question 6

discuss the function of each subunit of eIF4F complex

Answer 6

eIF4E = binds to m7G-CAP, limiting subunit
eIF4G = scaffold
eIF4A = helicase

Question 7

what is the initial recognition event that sets translation into motion?

Answer 7

cap complex eIF4F binds to mRNA cap

Question 8

what is the second initiation event?

Answer 8

eIF2 loads methionyl-tRNA onto small ribosomal subunit

Question 9

what % of translation starts w methionine?

Answer 9

95%

Question 10

which factors mediate the interaction between eIF4F and the small ribosomal subunit?

Answer 10

eIF1

eIF3

Question 11

what does the small ribosomal subunit do after binding to eIF4F?

Answer 11

scans along mRNA until the recognition of the start codon AUG

Question 12

what happens once the start codon is encountered by the small ribosomal subunit?

Answer 12

the initiation factors are release and the large ribosomal subunit binds (elongation commences)

Question 13

what is PABP?

Answer 13

poly A binding protein

interacts with polyA tail and cap binding complex

Question 14

why is PABP useful?

Answer 14

drastically improves translation of mRNA
keeps ribosomes/eIFs near?
circularization of ribosome bound mRNA

Question 15

how long is the polyA tail?

Answer 15

150-200 As

Question 16

what makes up the 60S subunit?

Answer 16

28S rRNA
5S rRNA
5.8S rRNA
49 proteins

Question 17

what makes up the 40S subunit?

Answer 17

18S rRNA

33 proteins

Question 18

what are the 3 sites on the ribosome?

Answer 18

A site: aminoacyl
P site: peptidyl
E site: empty

Question 19

what happens in the A site?

Answer 19

tRNA for the next codon enters

Question 20

what happens in the P site?

Answer 20

site of the growing peptide chain attached to tRNA

Question 21

how do toxins inhibit ribosome function?

Answer 21

rRNA N-glycosylase, cleaves N-glycosidic bond of adenine at position 432 in 28S rRNA
loss of protein synthesis results

Question 22

which toxins inhibit rRNA function?

Answer 22

shiga toxin (bacteria)
ricin toxin (castor bean)

Question 23

what factor is required for translocation/elongation?

Answer 23

EF2

Question 24

how does EF2 work?

Answer 24

hydrolyzes 1 GTP per translocation to move the ribosome

Question 25

what are diphtheria toxin and exotoxin A?

Answer 25

catalyze ADP ribosylation of EF2, blocking GTP hydrolysis
shuts down ALL translation
among the most toxic proteins that exist

Question 26

what is EF1?

Answer 26

elongation factor 1
escorts next tRNA to the vacant A site
hydrolyzes one GTP per amino acid

Question 27

what is important about the ester bond on the acceptor stem of a tRNA?

Answer 27

it is a high energy bond which is utilized in the formation of the peptide bond in protein synthesis

Question 28

what catalyzes the peptide bond formation?

Answer 28

peptidyl transferase

23S rRNA of the large ribosomal subunit is catalytic molecule

Question 29

what happens following peptide bond formation?

Answer 29

the nascent peptide shifts from P to A site

ribosome translocates to the next codon, moving the nascent peptide back to the P site

Question 30

what happens when the ribosome reaches the stop codon?

Answer 30

RF binds A site
catalyzes release of protein from tRNA
disassembly of ribosome with subunit recycling