Because the stop codon never occurs at the very end of the mRNA

Because the stop codon never occurs at the very end of the mRNA

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Because the stop codon never occurs at the very end of the mRNA, we find a 3' untranslated region or 3'UTR . A single mRNA molecule is not only translated once. In fact as soon as the ribosome has moved away from the initiation site, another round of initiation can begin (Fig. 7.14). It means that a single mRNA is often transcribed by many ribosomes at the same time, usually 100 to 200 bases apart from each other. Such a group of ribosomes on the same mRNA is called a polyribosome or polysome . However, at each single ribosome a polypeptide is synthesized independently. To fully understand the way translation occurs in E. coli , we have to remember two
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Unformatted text preview: additional things: prokaryotic mRNAs are often polycistronic in prokaryotes there is no nucleus that separates transcription from translation spatially Polycistronic mRNA means that it contains the coding region for several polypeptides (Fig. 7.6). In order for each coding region to be translated, it has to have all the specificities for translation: a Shine-Dalgarno sequence in front of an AUG start codon and a stop codon. No nucleus for spatial separation between transcription and translation in prokaryotes and translation starts near the 5' end of the mRNA (the end that is first synthesized in transcription)...
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This document was uploaded on 11/03/2011 for the course BIOLOGY MCB2010 at Broward College.

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