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Ribonucleic acid (RNA) is a sugar‑phosphate backbone that carries four nitrogenous bases: adenine (A), cytosine (C), guanine (G), and uracil (U). In messenger RNA (mRNA), these bases appear in codons—triplets of nucleotides—that specify the sequence of amino acids in a protein. For example, the codon AUG codes for methionine, which is universally the initiator amino acid in eukaryotic protein synthesis.
Ribosomes are the cell’s protein‑building factories, composed of two subunits that contain ribosomal RNA (rRNA) and proteins. Transfer RNA (tRNA) molecules ferry amino acids to the ribosome, binding at three distinct sites: the P (peptidyl) site, the A (aminoacyl) site, and the E (exit) site. The P site initially holds the methionine‑laden tRNA, while the A site receives the next tRNA during elongation, and the E site releases the empty tRNA.
Before translation, newly synthesized mRNA undergoes processing: a 5’ cap and 3’ poly(A) tail are added to protect the transcript, and introns are removed by spliceosomes. Initiation factors guide the small ribosomal subunit to the mRNA’s start codon, where it assembles with the large subunit, forming the translation preinitiation complex.
Translation commences when the preinitiation complex positions the methionine‑tRNA in the P site. The ribosome then scans along the mRNA, sequentially recruiting tRNAs that match each codon. As the ribosome moves, amino acids are linked into a growing polypeptide chain until a stop codon is encountered, prompting release of the newly synthesized protein.
