Chapter%2017

Chapter%2017 - From Gene to Phenotype: Transcription and...

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From Gene to Phenotype: Transcription and Translation
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TRANSCRIPTION TRANSLATION DNA mRNA Ribosome Polypeptide (a) Bacterial cell Nuclear envelope TRANSCRIPTION RNA PROCESSING Pre-mRNA DNA mRNA TRANSLATION Ribosome Polypeptide (b) Eukaryotic cell The Central Dogma of Molecular Biology: DNA makes RNA makes Protein
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Fig. 17-24 RNA polymerase DNA Polyribosome mRNA 0.25 µm Direction of transcription DNA RNA polymerase Polyribosome Polypeptide (amino end) Ribosome mRNA (5 end)
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DNA molecule Gene 1 Gene 2 Gene 3 DNA template strand TRANSCRIPTION TRANSLATION mRNA Protein Codon Amino acid RNA polymerase transcribes DNA into messenger RNA. Ribosomes translate information on mRNA into proteins.
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Second mRNA base First mRNA base (5 end of codon) Third mRNA base (3 Ribosomes read nucleotides of mRNA in groups of three, or codons. Each codon specifies one amino acid, except for the 3 codons that tell the ribosome to stop. The codon for methionine (AUG) can also act as a start codon.
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(a) Tobacco plant expressing a firefly gene (b) Pig expressing a jellyfish gene The genetic code is (more or less) universal.
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Promoter Transcription unit DNA Start point RNA polymerase 5 5 3 3 Initiation 3 3 1 RNA transcript 5 5 Unwound DNA Template strand of DNA 2 Elongation Rewound DNA 5 5 5 3 3 3 RNA transcript 3 Termination 5 5 5 3 3 3 Completed RNA transcript RNA Polymerase binds to a promoter region just 5’ to the region to be transcribed. Just like DNA, RNA is made only in the 5’ to 3’ direction. Eventually, transcription terminates, leaving an RNA copy of the gene.
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Elongation RNA polymerase Nontemplate strand of DNA RNA nucleotides 3 end Direction of transcription (“downstream”) Template strand of DNA Newly made RNA 3 5 5 Details of transcription
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A eukaryotic promoter includes a TATA box 3 1 2 3 Promoter TATA box Start point Template Template DNA strand 5 3 5 Transcription factors Several transcription factors must bind to the DNA before RNA polymerase II can do so. 5
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Chapter%2017 - From Gene to Phenotype: Transcription and...

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