translation 7.3. translation the information coded in mrna is translated to a polypeptide chain

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Translation 7.3 Translation the information coded in mRNA is translated to a polypeptide chain Transfer RNA (tRNA) nucleotides long some double-helical segments cloverleaf shape anticodon (sequence of 3 bases) is complementary to the codon on mRNA Aminoacylatio the addition of amino acids to the 3 end by aminoacyl-tRNA synthetase enzymes aminoacyl-tRNA = tRNA with corresponding amino acid attached Wobble Hypothesis tRNA can recognize more than one codon by flexible pairing between the first (5) base of the anticodon and third (3) base of the codon Ribosomes two subunits: large and small subunits clamp the mRNA between them Ribosome Binding Sites A site (aminoacyl site): incoming aminoacyl tRNA binds here P site (peptidyl site): where tRNA with the growing polypeptide is E site (exit site): where tRNA leaves the ribosome Translation initiation elongation termination Initiation the ribosome recognizes the 5 cap of the mRNA AUG (methionine) is always the first codon to ensure the correct reading frame Initiation Elongation the initiator tRNA (with methionine) enters the P site tRNA with the second amino acid enters the A site peptide bond forms between the methionine and the second amino acid (enzyme peptidyl transferase) Elongation the ribosome shifts one codon methionine tRNA is released (E site) second tRNA moves to the P site third tRNA enters the A site peptide bond is formed between the second and third amino acids elongation continues on in this manner Elongation Termination stop codons: UGA, UAG and UAA release factor protein binds to A site, polypeptide is released from P site, and the 2 subunits of the ribosome separate Animations Narrated animation with quiz: html Narrated animation (McGraw-Hill) with /student_view0/cha pter3/animation__how_translation_works.htm l Eukaryotes vs. Prokaryotes polysome = complex formed when multiple ribosomes attach to the same mRNA in prokaryotic cells, translation and transcription can happen at the same time Polypeptide to Protein the polypeptides are folded into their final protein form other modifications include addition of molecules such as sugars, assembling of mutiple polypeptide chains, etc.


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