The flow ofgeneticinformationmRNA to polypeptide chain of amino acid to formprotein within the cell in the presence of enzyme.
Explanation Inprokaryotes translation begins when the initial portion of an mRNA moleculebinds to rRNA molecule in a ribosome.the mRNA lies on the ribosomes in such away that only one of its codon is exposed at the polypeptide site at any time.A tRNAmolecule possessing the complementary three nucleotide sequence or anticodon,binds to the exposed codons on the mRNA are exposed at the series of tRNAmolecule bind one after another to the exposed codones. Each of these tRNAmolecules carries an attached amino acid, which is added to the end of thegrowing polypeptide chain.ParticulartRNA molecules become attached to specific amino acids through the action ofactivating enzymes called aminoacyl-tRNA synthetase , one of which exists foreach of the 20 common acids.
Polypeptidesynthesis begins with the formation of initiation copmplex. First a tRNA moleculecarrying a chemically modified methionine binds to small ribosomal unit.Proteins called initiation factor position the tRNA on the ribosomal surface atthe P site where peptide bond will form.
Nearby two other sites will form. Theinitiation complex , guided by another initiation factor , binds to AUG on themRNA.After theinitiation complex has formed , the large ribosome subunits binds tRNA moleculewith the appropriate anticodon appears, proteins called elongation factorsassist lie adjacent to each other undergo a chemical reaction , catalysed bythe large ribosomal subunit , which releases the initial methionine form itstRNA and attaches it instead by a peptide bond to the second amino acid.The ribosomenow moves three more nucleotides along the mRNA molecule in the 5′ to 3’direction , guided by other elongation factors. This movement translocates theinitial tRNA to the E site and eject from the ribosomes, repostions the growingpolypeptide chain to the p site , and exposes the next codon on the mRNA at theA site. When a tRNA molecule recognizing that codon appears, it binds to thecodon at the A site , placing its amino acid adjacent to the growing chain.
Thechain then transfers to the new amino acid, and the entire process is repeated.Elongationcontinues in this fashion until a chain terminating non sense codon is exposed.Nonsense codons do not bind to tRNA , but they are recognized by releasefactor, proteins that release the newly made plypeptide from the ribosome.