Notes on the Translation Process

Overview

Translation is the process in which ribosomes synthesize proteins using mRNA as a template. This involves three main steps:

Formation of Initiation Complex
- The small ribosomal subunit binds to the initiator tRNA.
- The initiator tRNA carries methionine (the initiator amino acid).
- This complex binds to the 5' cap of mRNA and scans for the start codon AUG.
- Mediated by several initiation factors.
Joining of Large Ribosomal Subunit
- At the start codon AUG, the large ribosomal subunit joins the complex.
- All initiation factors are released at this point.
Ribosome Sites
- A site: Entry site for new tRNA carrying amino acids.
- P site: Occupied by peptidyl tRNA carrying the growing polypeptide chain.
- E site: Exit site for tRNA after amino acid delivery.
- Initiator tRNA is positioned in the P site.

tRNA Entry and Anticodon Matching
- A new tRNA with an amino acid enters the A site.
- The anticodon of tRNA is matched against the mRNA codon.
- Incorrect tRNA are rejected; correct tRNA are accepted.
Peptide Bond Formation
- A peptide bond forms between adjacent amino acids.
- The tRNA in the P-site transfers its amino acids to the tRNA in the A-site.
Ribosome Translocation
- Ribosome moves forward on the mRNA.
- Empty tRNA moves to the E site and exits.
- Peptidyl tRNA moves to the P site.
- A-site is vacant for the next tRNA.
Cycle Repetition
- This cycle repeats for each codon on the mRNA.

Recognition of Stop Codons
- Termination occurs when a stop codon enters the A site.
- No tRNA matches stop codons; instead, they are recognized by a release factor.
Polypeptide Release
- Binding of the release factor cleaves the bond between the polypeptide and tRNA.
- The polypeptide is released from the ribosome.
Ribosome Disassociation
- The ribosome disassociates into subunits.
- Ribosome is then ready for a new round of translation.