Because 3 of the 64 genbank possible codons are stop

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Unformatted text preview: 1 (0 ORF) 2nd (+1 ORF), or 3rd (+2 ORF) nucleotides. Each three of these possibilities is called a reading frame: an Open Reading Frame (ORF) is a long reading an Open stretch of DNA that can be read without encountering a stop codon. ORFs are considered DNA stop ORFs candidate for protein-coding exon regions: the inferred amino-acid sequence can be compared with GenBank to identify possible analogous proteins. Because 3 of the 64 GenBank possible codons are stop codons, a stop codon should occur at random approximately every 20 codons: the occurrence of multiple stop codons in a particular reading frame indicates 20 the that it does not code for a polypeptide. Ordinarily, only one reading frame is open. BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 12 Requirements for Translation ­ mRNA (codons) ­ Ribosomes ­ Transfer RNA (tRNA) ­ Aminoacyl synthetase ­ Amino acids ­ Initiation, elongation and termination Initiation, factors factors ...
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