FRANCIS LEROY & JANA HERMANOVA, BIOCOSMOS / SCIENCE PHOTO LIBRARY FRANCIS LEROY & JANA HERMANOVA, BIOCOSMOS / SCIENCE PHOTO LIBRARY
Animation showing the process of protein synthesis in prokaryotes (such as bacteria). This process is knows as translation. It occurs in ribosomes, whose 30S subunits have three active sites, labelled E, P and A. Two initiation factors (If-3, blue, and If-1, green) bind to the ribosomal subunit. A third initiation factor, IF-2 (red) is attached to GTP and fMet-tRNA, which carries an UAC anticodon to the ribosome. This binds to the AUG start codon on the mRNA in the ribosome's P site. The initiation factors depart and a 50S subunit joins the 30S subunit to form a 70S subunit. The GTP is hydrolysed to GDP and inorganic phosphate, and the next amino acid (Leu, green) in the growing protein chain arrives on its tRNA. This forms a peptide bond (yellow) with the fMet, which detaches from its tRNA, which leaves the E site. Another tRNA then brings the next amino acid (Arg, green) to the A site, and the process continues, building a long chain of amino acids. The process terminates when a termination codon (UAG) enters the A site, which is not recognised by a tRNA, and instead binds to a Release factor (Rf1, purple). This releases the protein chain and the complex dissasembles.
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