How do ribosomes assemble amino acids into a protein chain?

Ribosomes assemble amino acids into protein chains through a process called translation, which occurs in several coordinated steps.12

The Assembly Process

1. Initiation: The process begins when messenger RNA (mRNA) binds to the smaller subunit of the ribosome. A specific transfer RNA (tRNA) carrying an amino acid binds to the mRNA, followed by the attachment of the larger ribosomal subunit.2
2. Elongation: The ribosome reads the mRNA in "words" of three nucleotides called codons. For each codon, a specific tRNA molecule—carrying the corresponding amino acid—binds to the ribosome's aminoacyl-acceptor (A) site.12
3. Peptide Bond Formation: The ribosomal RNA (rRNA) within the larger subunit catalyzes the peptidyl transferase reaction. This forms a peptide bond between the amino acids, linking them into a growing chain.34
4. Translocation: The ribosome moves along the mRNA by one codon. The tRNA that has donated its amino acid is released, and the growing peptide chain shifts to the peptidyl-donor (P) site, leaving the A site open for the next tRNA.2
5. Termination: This cycle repeats until the ribosome encounters a termination codon (UAG, UAA, or UGA). At this point, the completed protein is released, and the ribosomal complex dissociates.12