Protein Synthesis Flashcards
How do amino acids bind to their cognate tRNA?
amino acid + ATP —> a. acid AMP complex + ADP + Pi
- catalysed by tRNA synthase
What are the 3 processes of protein synthesis?
- Initiation @ start codon
- Elongation
- Translocation @ stop codon
Describe the process of Initiation.
1 - Small subunits join to form complexes with initiation factors, base pairing occurs between the small subunit + a special sequence on the mRNA
2 - Start codon of mRNA positioned in the ribosomal P site + formylmethionyl tRNA joins
3 - Large subunit joins, GTP is hydrolysed + initiation factors leave ribosome
What is GTP?
Guanosine Triphosphate - source of energy in protein synthesis
Describe the Elongation process.
The ribosome has 3 sites where tRNA can bind, but only 2 are normally occupied at once. These require elongation factors.
- A Site = Aminoacyl Acceptor Site = IN
- P Site = Peptidyl Site = BOND FORMATION
- E Site = Exit Site = OUT
What does EFTu do?
Catalyses the delivery of aminoacyl tRNA to the ribosome
What does EFG do?
Catalyses translocation (the movement of tRNA and mRNA through the ribosome)
What are the 2 elongation factors involved in this process?
EFTu - catalyses binding of aminoacyl-tRNA to the ribosome
EFG - catalyses movement of tRNA and mRNA through the ribosome
Describe the Translocation process.
- Ribosome moves one codon towards 3’ end of the mRNA = Growing peptide chain can move from A to P site
- Unloaded tRNA now moves to the E site
- A site now empty
- Process will repeat until stop codon reached
What happens when the stop codon is reached?
- A special release factor binds to the A site
- the polypeptide in the P site is hydrolysed from its tRNA.
- tRNA exits ribosome via E tunnel
What happens after protein synthesis (polypeptide chain is synthesised)?
Post-Translational Modification (PTM)
What is PTM?
The enzymatic (covalent) modification of a protein after its translation to give different versions of the same gene.
What are the 4 common types of PTM?
- Lipidation
- Phosphorylation
- Glycosylation
- Acetylation
What does a combination of splicing and PTM do in the body?
Converts genome into transcriptome (splicing)
Converts transcriptome into proteome (PTM)
What is splicing?
splitting mRNA
What does a genome consist of?
> 25,000 genes
What does a transcriptome consist of?
> 100,000 RNA transcripts
What does a Proteome consist of?
> 1 million proteins
Why is PTM important?
- Fundamental in the activity, localisation + interaction of proteins with other cellular molecules.
- Modifications have significant effects of protein struct. + function so can be used in therapeutic/diagnostic use
What happens in PTM phosphorylation?
Kinase adds phosphate group
- Critical in the regulation of many cellular processes
What happens in PTM glycosylation?
Protein: - folding - conformation - distribution - stability - activity (Freya came determined so achieved)
When does PTM occur?
At any step of ‘life cycle’ of a protein.
- Many modified shortly after translation to mediate proper folding + stability or to direct protein to different places in the cell
- Other mods. occur after folding to activate/inactivate activity
