Translation Elongation

Question 1

What are the steps of translation elongation?

Answer 1

1) Entry of aminoacyl-tRNA
2) Peptide bond formation and transfer
3) Translocation

Question 2

During elongation, what are the elements in the SSU?

Answer 2

• In the SSU: anticodons of current and incoming tRNA

Question 3

During elongation, what are the elements in the LSU?

Answer 3

• In the LSU: growing peptide and AA of tRNA

Question 4

What is translocation?

Answer 4

release of uncharged tRNA (which is in the P site)

Question 5

Where do the AA-tRNA enter?

Answer 5

Into the empty A site

Question 6

Describe briefly the amino acid transfer.

Answer 6

From P site to A site (the peptide attaches to the new AA on tRNA)
o Peptide now in the A site then moves to the P site

Question 7

What factors are involved in the entry of AA-tRNA?

Answer 7

EF-Tu and EF-Ts

Question 8

What are the roles/activity of EF-Tu?

Answer 8

o Has GTPase activity (it binds GTP)
o Exists in 2 states
 Ef-Tu(GTP): activated (bound to GTP)
 Ef-Tu(GDP): inactivated (bound to GDP)
o The binding site of the activated EF-Tu is adjacent to the A site
 Facilitates the docking of AA-tRNA into the correct position on the ribosome
o The inactive EF-Tu is released
 The energy released activates the AA-tRNA to form a peptide bond

Question 9

What are the roles/activity of EF-Ts?

Answer 9

o Facilitates the binding of GTP on Ef-Tu

o Reactivates Ef-Tu to recycle it

Question 10

Describe the peptide bond formation and transfer.

Answer 10

• Activated *NH3 is an active nucleophile
• It attacks the C=O of the growing peptide
• The growing peptide thus transfers from P to A
o The peptide attaches to the new AA on tRNA

Question 11

What is the point of translocation?

Answer 11

• During translocation, the ribosome is moved 3 nucleotides forward from 5’ to 3’ (to the next codon)
o The deacylated (empty) tRNA is released

Question 12

What are the steps in translocation?

Answer 12

1) LSU “tilts” forward, creating 2 hybrid sites
 LSU E / SSU P : contains the deacylated tRNA
 LSU P / SSU A : contains the peptidyl tRNA
2) SSU tilts forward
 Intact E: contains deacylated tRNA (which will be expelled)
 Intact P: P-tRNA
 Intact A: empty

Question 13

What factors are involved in translocation?

Answer 13

EF-G

Question 14

What is the role of EF-G in translocation?

Answer 14

o EF-G
 Exists in 2 states
• EF-G (GTP) : activated
• EF-G (GDP) : inactivated
 Binds the same site as EF-Tu (adjacent to A site)
 Causes conformational change (hybrid movement)