Transcript Stages and mechanisms of translation, regulation of translat

Stages and mechanisms of
translation, regulation of
translation. Antibiotics –
ingibitors of transcription
and translation
STAGES OF TRANSLATION
• 1. Recognition
• 2. Initiation
• 3. Elongation
• 4. Termination
RECOGNITION
O
R1
CH
COOH + H O
O
P
O
P
OH
NH 2
O
O
OH
P
O Аденозин
OH
O
R1
CH
CO
O
P
O
Аденозин + H4P2O7
OH
NH 2
Aminoacyladenilate
Aminoacyl-tRNA-synthetase
Aminoacyladenilate + tRNA  aminoacyl-tRNA + AMP
Activation of amino acids
Each amino acid has a specific tRNA
There is specific aminoacyl-tRNA-synthetase for each AA
The
structure
of tRNA
Initiation of Translation
• The translation complex is assembled
at the beginning of the mRNA coding
sequence
• Complex consists of:
-Ribosomal subunits
-mRNA template to be translated
-Initiator tRNA molecule
-Protein initiation factors
Initiator tRNA
• First codon translated is usually AUG
• The initiator tRNA recognizes
initiation codons
-Bacteria: N-formylmethionyl-tRNA
-Eukaryotes: methionyl-tRNA
Initiation
of protein
biosynthesis
MethionylтRNA
binds to Pcenter
Sites for tRNA binding in
ribosomes
There are two
centers:
peptidyl (P)
and
aminoacyl (А)
Elongation
1) Positioning of the next
aminoacyl-tRNA
in the A site
2) Formation of the
peptide bound
(enzyme – peptidyl
transferase) between
methionine and AA in Acentre. The residue of
methionine is transferred on
the amino group of another
AA
3) Translocation – shift of
ribosome by one codon.
Methionyl-tRNA is released
from P-centre. DipeptidyltRNA moves from A-centre
to P-centre.
Termination of
Translation
• Ribosome comes to terminal codon UGA,
UAG or UAA
• No tRNA molecules recognize these
codons and protein synthesis stalls
• Protein termination factors F-1, RF-2,
RF-3 split off synthesized polypeptide
from the last tRNA
• Ribosomal complex dissociates
Termination of
Translation
POSTTRANSLATIONAL MODIFICATION
1) Preparing of proteins for different functions
2) Direction of proteins to different locations (targeting)
1. Removing of methionine (formylmethionine)
2. Formation of disulfide and other bonds (secondary,
tertiary structures)
3. Proteolytic cleavage
4. Modification of amino acid residues:
- Hydroxylation
- Glycosilation
- Phosphorilation
5. Joining of prosthetic groups or cofactors
6. Formation of the quaternary structure
Regulation of the Protein Biosynthesis
The operon model (by Jacob and Monod)
Inhibitors of Transcription
Antibiotics
inhibiting protein
synthesis