Translation: Building the Protein

🏭 Translation: Building the Protein

Where it happens: At the ribosome, in the cytoplasm.

Translation is the process by which the sequence of bases in mRNA is used to assemble a specific sequence of amino acids — a polypeptide chain that will fold into a protein. The ribosome is the molecular machine that performs this reading.

Step-by-step: what happens during translation

1. The mRNA strand threads through the ribosome.
2. The ribosome reads the mRNA in groups of three bases called codons. Each codon specifies one amino acid (or a start/stop signal).
3. Transfer RNA (tRNA) molecules carry specific amino acids to the ribosome. Each tRNA has:
   • An anticodon — a sequence of three bases complementary to the mRNA codon
   • An amino acid attached to its other end
4. A tRNA with the complementary anticodon binds to the mRNA codon at the ribosome by hydrogen bonds.
5. The ribosome catalyses the formation of a peptide bond between the incoming amino acid and the growing polypeptide chain.
6. The tRNA detaches and returns to the cytoplasm to pick up another amino acid.
7. The ribosome moves along the mRNA to the next codon (in the 5'→3' direction).
8. Steps 3-7 repeat until a stop codon (UAA, UAG, or UGA) is reached — no tRNA matches a stop codon, so translation ends.
9. The completed polypeptide chain is released and folds into its specific three-dimensional shape, becoming a functional protein.

Key rule — codon/anticodon pairing: The tRNA anticodon is complementary to the mRNA codon. If the codon is AUG, the anticodon is UAC. Hydrogen bonds hold them together during translation.