DB Lecture 26: Translation Machinery and Mechanism I

Question 1

What is the “wobble” position?

Answer 1

the third amino acid in a codon that can be variable for some amino acids and does not require the usual complementarity

Question 2

What is tRNA?

Answer 2

the link between mRNA and protein

Question 3

What are the zones of tRNA?

Answer 3

DUH arm
anticodon arm (anticodon sequence)
V loop
T!C arm
discriminator nucleotide
CCA cap (3' end)
cognate amino acid

Question 4

What initiates translation?

Answer 4

a special form of methionyl tRNA

Question 5

What is aminoacyl tRNA synthase?

Answer 5

the enzyme that attaches an amino acid to its cognate tRNA

Question 6

What performs translation?

Answer 6

ribosome (large and small subunits)- each subunit contains dozens of proteins and a large quantity of rRNA

Question 7

What are the sites on a ribosome?

Answer 7

E-site (exit site)- where the tRNA in the P site goes after its peptide cargo has engaged in peptide bond synthesis
P-site (peptidyl site)- where the tRNA with the growing peptide chain is located
A-site (aminoacyl site)- where the next charged tRNA binds

Question 8

What are eIFs?

Answer 8

eukaryotic initiation factors (eIFs)

bind the ribosome to the mRNA 5’ end and position the ribosome to initiate translation

Question 9

What is an eRF?

Answer 9

eukaryotic release factor
is required for release of the finished polypeptide upon encountering a stop codon
required for the release of the ribosome from the mRNA

Question 10

What is an eEF?

Answer 10

eukaryotic elongation factor
participate in bringing succeeding charged tRNA to the site on the ribosome
translocation of the ribosome to the next codon

Question 11

List the components of the 43S pre-initiation complex.

Answer 11

40S ribosome subunit (eIF1,3,5)
numerous eIFs
complex of Met-tRNAi and eIF2 in its GTP-bound state

Question 12

List the eukaryotic translation factors.

Answer 12

eIF
eEF
eRF

Question 13

What are the steps of translation?

Answer 13

formation of the pre-initiation complex (43S), initiation, elongation, and termination

Question 14

What composes ribosomes?

Answer 14

some protein
40S (large) and 60S (small) subunits
combine to make a 80S which is all composed of rRNA

Question 15

Describe the sequence of events for initiation (translation).

Answer 15

eIF4 binds to 5’ cap and recruits 43S complex, which scans down mRNA (using ATP) until the AUG (start codon) is found in the proper context
GTP hydrolysis of eIF2 (via eIF5 on the 43S) results in it dissociating from the complex
all other eIF units leave
80S ribosome component 60S (guided by eIF5B) binds to UAC and Met-tRNA (at the P site)
eIF5B leaves the complex