RNAProtein160-page12 - The polypeptide chain always...

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Gene Expression – DNA to Protein - 12 Elongation The next tRNA molecule, with its attached amino acid, is brought into place at the ribosome's A site with the assistance of elongation factors according to the mRNA codon message. The tRNA anticodon will hydrogen bond to the mRNA codon at this time. The positioning of the two tRNA molecules (each with its proper amino acid) at the P and A sites is such that a peptide bond can be formed between the two amino acids that are attached to their respective tRNAs. rRNA functions as a ribozyme to catalyze the peptide bond between the amino acid from the P site to the amino acid at the A site at the peptide bonding site on the ribosome. This process detaches the P site amino acid from its tRNA; the first amino acid attaches to the second amino acid at the A site.
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Unformatted text preview: The polypeptide chain always elongates at the A site. Once the peptide bond is formed, the A-site tRNA will shift to the P site and the P site tRNA will shift to the E site and be dislodged from the ribosome (which is why the E site is called the exit site). A new tRNA that matches the 3 rd mRNA codon will be brought into the now vacant A site by elongation factor proteins. The codon-anticodon binding, peptide bonding, detachment of tRNA and shifting continues until all of the codons of the mRNA have been matched by tRNA anticodons. The mRNA moves along the ribosome with its 5' cap leading. mRNA moves only in one direction. Ribosomes and mRNA move relative to each other, codon by codon, unidirectionally....
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This note was uploaded on 12/29/2011 for the course BIO 151 taught by Professor Edwards during the Spring '10 term at SUNY Stony Brook.

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