During protein synthesis (translation), the ribosome acts as a crucial platform where mRNA is decoded and amino acids are linked together to form a polypeptide chain. Two key sites on the ribosome, the A site and the P site, play distinct roles in this process.
The A site, short for Aminoacyl-tRNA binding site, is the location on the ribosome where incoming charged tRNAs (tRNAs carrying amino acids) initially bind. It's the 'entry point' for each new amino acid that will be added to the growing polypeptide chain.
The P site, or Peptidyl-tRNA binding site, is where the tRNA holding the growing polypeptide chain is located. It's the 'home base' for the peptide as it's being assembled.
| Feature | A Site | P Site |
|---|---|---|
| Full Name | Aminoacyl-tRNA binding site | Peptidyl-tRNA binding site |
| Function | Accepts incoming aminoacyl-tRNA | Holds the tRNA with the growing polypeptide chain |
| tRNA Binding | Binds to charged tRNA carrying a single amino acid | Binds to tRNA attached to the peptide chain |
| Peptide Bond Formation | Amino acid from A site tRNA attacks the peptide on the P site tRNA to form a new peptide bond. | Peptide chain is transferred to the amino acid on the A site tRNA. |
| Location after Translocation | Becomes the new P site | Leaves the ribosome (after transferring the peptide to the A site tRNA) |
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