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9. Transcription

This transcription guide explores the process of converting DNA into RNA, and then translating the RNA code into proteins. Learn about transcription factors, gene structure, alternative transcripts, and the control of gene expression. Discover the role of transcription factors in enhancing or repressing gene expression through DNA binding.

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9. Transcription

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  1. 9. Transcription Chapters 26 Lehninger 5th Edition http://www.steve.gb.com/science/transcription.html

  2. Transcription • DNA -> RNA • Translation • RNA -> Protein

  3. Genes • 1 gene -> 1 protein? • Transcription • Read a gene from the DNA • DNA -> RNA • Translation • Translate the DNA code to protein code • RNA -> Protein

  4. Transcription • RNA Polymerase • Reads DNA • Makes RNA copy of • One strand • One gene

  5. Transcription • Open DNA at promoter • Make RNA • 5’-> 3’ • transcription bubble • Moves along gene • Prevent DNA knotting • DNA topo-isomerases

  6. Transcription • Initiation • At promoters • Control by Transcription Factors • “Gene expression” • Termination • Processing of the transcript (Eukaryotes) • e.g. remove introns, add stuff to ends, modify bases • Final product • e.g. mature mRNA or mature miRNA

  7. Bacterial Promoters • Simple • Fixed spacing of binding sites • Transcription factors

  8. Transcription Factors Bind DNA

  9. Bacterial Gene Structure • Simple promoter close to start of transcript • Gene transcribed as one piece of mRNA • Transcription terminates • Terminator signal • Ready to translate m

  10. Bacterial Operons • Genes may be grouped in Operons • Co-regulation • Single transcript

  11. Eukaryotic Gene Structure • V. complicated promoters • e.g. Human: • 2000 TFs • Spread over 10s of kb • Several kb from coding region • Pieces of mRNA removed before translation • Introns • Rich Roberts, Phil Sharp

  12. Eukaryotic gene processing • Remove introns • Splicing • Add 5’ cap • Cleavage of 3’ end of mRNAat polyA site • Add 3’ polyA tail

  13. Alternative transcripts • Alternative polyA sites • Alternative splicing • Alternative exons • Alternative promoters

  14. Alternative polyA

  15. Alternative splicing

  16. RNA Genome? • Central dogma: • DNA -> RNA -> protein • RNA Virus • e.g. HIV: • RNA -> DNA • Reverse transcriptase

  17. What Controls Gene Expression? • Transcription factors • Regulatory RNAs • miRNA • smRNA • siRNA • Methylation • Chromatin

  18. Transcription Factors • Proteins which bind DNA • Enhance or repress gene expression • Families e.g.: • Homeodomain (Hox) • POU domain (Oct-1) • Helix-loop-Helix (c-Myc) • Zinc Fingers (TFIIIA) • Leucine Zipper (c/EBP) • Winged Helix (Fox family) • Helix Turn Helix • At least 10% of genes in Human genome are TFs

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