1. Translation III: The mechanism of protein synthesis
Edited by Gergely Berta

2. The steps of initiation
Initiation factors B
P-site
(peptidyl-tRNA binding site)
A-site
(aminoacyl-tRNA binding site) C
50S
fMet
formylmethionyl-tRNA
30S
anticodon
2 codons 5’
A U G
mRNA
Ribosome binding sequence

3. N-formylmethionyl-tRNA
formyl group C
HN-CH-C O O R1 A O
Blocked amino acid → it can be used only at the beginning, i.e. at the N-terminus
The formyl group is removed by deformylase during elongation
Aminopeptidase removes methionine
Eukaryotes: no formylation

4. Elongation of the translation
E-site (exit-site) B
P-site
(peptidyl-tRNA binding site)
A-site
(aminoacyl-tRNA binding site) C
fMet
Aa2 EF 5’

5. B.: formation of the peptide bond
P-site
A-site
Peptidyl transferase cuts (hydrolyzes) the ester bond between the amino acid and the tRNA in the P-site
Energy is released
The carboxyl group of the amino acid in the P-site can now bind to the amino group of the amino acid in the A-site
The peptide bond is created O H H O O O C
HN-CH-C C
HN-CH-C
N-CH-C
H2N-CH-C O O O H O O R1 H R1 R2 R2 A A A O O O

6. Termination of the translation
aan
aan-1
aan-2
aan-3
aan-4
aan-5
aan-6
aan-7
aan-8
aan-9
releasing
factor
stop codon

7. 3D structure http://publications.nigms.nih.gov
www_wadsworth.org_joachim_frank.jpg

8. Eukaryotic translation
Localisation of the ribosomes:
Free ribosomes in the cytoplasm, they synthetise:
Proteins of the cytosol
Proteins of the nucleus
Proteins of the mitochondria
Bound ribosomes on the surface of the rough endoplasmic reticulum:
Secretory proteins
Proteins of the rough ER
Proteins of the Golgi-apparatus
Proteins of the lysosomes
Proteins of the cell membrane

9. General features of translation
Direction: 5’→3’ (mRNA)
N-Terminus → C-Terminus (polypeptide chain)
Polysomes are formed
one polypeptide chain/ ribosome
The 3D structure of the protein chain is being already formed during translation

10. Inhibitors of protein synthesis
In prokaryotes:
Chloramphenicol peptidyl transferase
Erythromycin translocation
Tetracyclin aminoacyl-tRNA binding
Streptomycin S subunit
What is the relevance?
These are used as antibiotics against bacterial infections
They have side-effects:
Mitochondrial translation is also inhibited
If they are not specific enough for prokaryotes
They influence other proteins/mechanisms in the eukaryotic cells