Translation (Protein Synthesis)
PROTEIN SYNTHESIS
Translation
Conversion of mRNA to protein
Codon
Group of three mRNA nucleotides that encode one amino acid
Ribosomal Structure
- 2 subunits each made of protein and RNA:
- E-site (Exit site)
- P-site (Peptidyl-tRNA binding site)
- A-site (Aminoacyl-tRNA binding site)
Initiation
- Initiator t-RNA (methionine) binds to small ribosomal subunit (with help from initiation factors)
- Small ribosomal subunit/initiator t-RNA complex binds mRNA (using 5' cap to bind the 5' end)
- Complex scans towards the 3' end until it locates the start codon (AUG which sets the appropriate reading frame) and the large ribosomal subunit arrives
Elongation
- Current tRNA in the P-site
- New tRNA added to A-site
- Growing peptide chain added to amino acid bound to A-site tRNA
- Large ribosomal subunit shifts 3' one codon
- Small ribosomal subunit follows - tRNA that was in P-site now in E-site and tRNA that was in A-site now in P-site
- E-site tRNA ejected and new A-site tRNA added
Termination
- When codon in A-site is stop codon (UAG, UAA, or UGA) a release factor is added to the A-site
- Release factor binding releases the peptide chain and causes ribosome to dissociate