Translation

Question 1

What is aminoacyl-tRNA synthetase?

Answer 1

Aminoacyl-tRNA synthetase attaches amino acid to the corresponding tRNA on the 3’OH of the ribose in tRNA – requires ATP.

There are specific aminoacyl-tRNA synthetase

Question 2

What are the 3 binding sites in ribosomes?

Answer 2

A site (new aminoacyl-tRNA joins)

P site (where the first tRNA joins & where peptidyl-tRNA is held)

E site (where ribosome moves and the uncharged tRNA moves into).

Question 3

What are the steps in translation initiation?

Answer 3

IF1,2,3 bind to start codon which recruits the 1st tRNA to the P site.
GTP is hydrolysed by IF2 which causes the large and small ribosomal subunits to join

Forms the initiation complex.

Question 4

What are the steps in translation elongation?

Answer 4

2nd aminoacyl-tRNA joins A site and peptide bond forms between 1st and 2nd amino acids.
Growing polypeptide is held by the the 2nd tRNA.

Ribosome moves one step and the uncharged tRNA is now at the E site, and the peptidyl tRNA is at the P site.

EF-TU binds the A site and hydrolyses GTP causing new aminoacyl-tRNA to bind to the A site; EF-TU is released. EFG binds to tRNA and hydrloyses GTP to allow ribosome to move.

Question 5

What does tetracycline do?

Answer 5

Inhibits aminoacyl-tRNA binding

Question 6

What does erythromycin do?

Answer 6

Binds to the peptidyl transferase site and blocks polypeptide exit from ribosome

Question 7

What does chloramphenicol do?

Answer 7

Blocks correct positioning of the aminoacyl-tRNA; inhibits peptidyl transferase reaction in the large subunit

Question 8

What does ricin do?

Answer 8

Prevents activation of translation factor GTPases (EF-TU), so prevents new tRNA attaching to ribosome. It targets both eukaryotic and prokaryotic cells.

Question 9

What does Diptheria toxin do?

Answer 9

Acts on eukaryotic elongation factor. It couples ADP-ribose to the elongation factor to inactivate it

Question 10

Bacterial ribosome

Answer 10

70S ribosomes

Large 50S: 34 proteins, 2 RNAs (5S rRNA + 23S rRNA) – contains peptidyl transferase centre + ribosomal exit tunnel. Function: peptide bond formation

Small 30S: 21 proteins, 1 RNA (16S rRNA) – binds translation; correct translation occurs here

Question 11

Eukaryotic ribosome

Answer 11

80S ribosomes

Large 60S: 49 proteins, 3 RNAs (5S rRNA, 5.8S rRNA, 23SrRNA)

Small 40S: 33 proteins, 1 RNA (18S)