CH 7 From DNA to protein How cells

CH 7 From DNA to protein How cells - Chapter 7 From DNA to...

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1 Chapter 7 From DNA to protein: How cells read the genome Part 1: Transcription
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2 Transcription provides amplification of genetic information Genes can be transcribed with very different efficiencies Transcription produces RNA complementary to one strand of DNA 5’-AGGTCCACG-3’ 3’-TCCAGGTGC-5’ DNA Template strand Transcription (5’ to 3’) 5’-AGGUCCACG-3’ RNA
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3 Transcription A small portion of DNA helix must be opened and unwound to expose the bases on each strand RNA is synthesized by RNA polymerase • Nucleotides added to 3’ end of RNA strand (5’ to 3’) • RNA sequence is dependent on complementary base pairing (A-U, G-C) No primer is needed The complementary RNA strand is released from the DNA template strand almost immediately. This allows another RNA polymerase molecule to initiate even before the first is competed. RNA polymerase error rate is 1 in 10 4 . Compare to DNA pol Transcription of DNA by RNA polymerase
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4 Genes can be simultaneously transcribed by many RNA polymerase molecules Amplification of genetic information Direction?
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5 What controls where RNA polymerase initiates and terminates transcription? Promoter: DNA sequence that is recognized by RNA polymerase as a start point. Chain elongation occurs until RNA polymerase reaches a terminator site , at which RNA is released and the RNA polymerase dissociates from the DNA 07_09_1_bacterial gene.jpg
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6 07_09_2_bacterial gene.jpg Promoters are asymmetrical so RNA polymerase transcribes in only one direction Both strands can serve as a template for RNA polymerase
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7 Transcription in eukaryotes differs from prokaryotes 1. RNA polymerase • Prokaryotes have a single type • Eukaryotes have three types RNA pol I: most rRNA genes RNA pol II: protein-encoding genes (makes mRNA) RNA pol III: tRNA, 5S rRNA, small structural RNA genes 2. Initiation • Prokaryotic RNA pol can initiate without helper proteins • Eukaryotic RNA pols require general transcription factors 3. Transcript processing • Prokaryotic transcripts are generally NOT processed • Eukaryotic mRNAs are processed TATA-binding protein (TBP) is a subunit of TFIID Assembly of transcription initiation complex Phosphorylation of RNA Pol II by TFIIH, transcription proceeds Transcription initiation RNA pol II
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8 Phosphorylation of RNA Pol II by TFIIH also allows RNA processing proteins to assemble on its tail
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CH 7 From DNA to protein How cells - Chapter 7 From DNA to...

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