13 BIO 326R Translation feb 23

13 BIO 326R Translation feb 23 - BIO 326R Translation...

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Unformatted text preview: BIO 326R Translation February 23 Reading frames Every sequence of DNA has 3 different reading frames (or 6 if you read both strands) A reading frame is open until a stop codon is reached Productive open reading frames (i.e. sequences that are eventually translated) almost always start with an AUG codon (Methionine) Note that the RNA polymerase does not recognize frames or codons!!! It transcribes one base at a time, it transcribes AUG just as well as UGA Reading frames end with a stop codon, UGA, UAG, UAA. There are 3 stop codons out of 64 total codons. Thus, assuming a somewhat random DNA sequence, a stop codon is expected about every 20 codons/60 bases. Protein encoding segments will deviate from this in the correct frame. Transcription unit Termination site ORF Codes for protein Promoter 5 UTR 3 UTR ORF : Open Reading Frame sequence of DNA with no stop codon Or: sequence from a start codon to the nearest in-frame stop codon UTR : Untranslated Region Termination site site where RNA polymerase falls off DNA Bacterial genes may be polycistronic, ie encode more than one ORF so that different polypeptides can be made from a single mRNA DNA RNA mRNA monocistronic and polycistronic AUG UGA or UAG or UAA 5 UTR leader 3 UTR trailer Ribosome binding site...
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13 BIO 326R Translation feb 23 - BIO 326R Translation...

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