Summary
Highlights
Translation is a crucial part of protein synthesis, the process by which cells create proteins. Protein synthesis has two stages: transcription (in the nucleus of eukaryotic cells) and translation (at ribosomes). Ribosomes are found either attached to the rough endoplasmic reticulum or free in the cytoplasm in eukaryotic cells, and only in the cytoplasm of prokaryotic cells.
The function of translation is to decode mRNA to build a polypeptide chain, which is a long chain of amino acids that folds into a functional protein. This process utilizes tRNA molecules to bring the correct amino acids to the ribosome, matching the mRNA sequence.
Translation begins when a ribosome attaches to an mRNA strand at the start codon, a specific three-base sequence (often AUG). A tRNA molecule with a complementary anticodon (e.g., UAC) binds to the start codon, carrying a specific amino acid, such as methionine.
A second tRNA molecule with an anticodon complementary to the next mRNA codon binds. The two amino acids are then linked by a peptide bond, a process requiring ATP. Only two tRNA molecules can attach to the ribosome at any given time, so the first tRNA detaches after forming the bond, leaving its amino acid behind. The ribosome then moves to the next codon, allowing more tRNAs to bind and add amino acids, elongating the polypeptide chain.
This elongation continues until the ribosome encounters a stop codon on the mRNA strand. A stop codon does not code for an amino acid; instead, it signals the end of the translation process. Once the stop codon is hit, the completed polypeptide chain detaches from the ribosome, and translation is complete.
After detaching, the polypeptide chain folds into a specific three-dimensional shape and may combine with other polypeptides. This folded structure forms a functional protein ready for use in the body. Polypeptide chains can be thousands of amino acids long.