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Unformatted text preview: mutations induced by mutagens should be single nucleotide substitutions and conform to the code. Fig. 8.10 a Genetic code is almost universal but not quite All living organisms use same basic genetic code.
Translational systems can use mRNA from another organism to generate protein. Comparisons of DNA and protein sequence reveal perfect correspondence between codons and amino acids among all organisms. Transcription RNA polymerase catalyzes transcription. Promoters signal RNA polymerase where to begin transcription. RNA polymerase adds nucleotides in 5' to 3' direction. Terminator sequences tell RNA when to stop transcription. (UAA, UAG,UGA) Initiation of transcription Fig. 8.11 a Elongation Fig. 8.11 b Termination Fig. 8.11 c Information flow Fig. 8.11 d Promoters of 10 different bacterial genes Fig. 8.12 In eukaryotes, RNA is processed after transcription A 5' methylated cap and a 3' Poly-A tail are added. Structure of the methylated cap How Poly-A tail is added to 3' end of mRNA Fig. 8.14 RNA splicing removes introns Exons sequences found in a gene's DNA and mature mRNA (expressed regions) Introns sequences found in DNA but not in mRNA (intervening regions) Some eukaryotic genes have many introns. Dystrophin gene underlying Duchenne muscular dystrophy (DMD) is an extreme example of introns Fig. 8.15 How RNA processing splices out introns...
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