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Regulacao transcricao
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Regulacao transcricao

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  • UAS- upstream activation sequence Introns – also in yeast, though not so many
  • Go over table: mention how it was a surprise to many that the human genome really did not contain more genes than a weed or even a worm, and that for most multicellular organisms the number of genes does not correspond to the relative complexity of the organism. One of the clear differences is gene density; that is, how much space between genes and how much space over which a gene is spread out.
    The bottom statement. Discuss how even though every cell has all genes, every cell is not identical in the body. This raises the question of how, given that a liver cell has all genes, does it know to become a liver cell? The answer lies in large part in that not all genes are “turned on” in any given cell type. Of course, this answer then begs the question of how does the cell know which genes to turn on and keep off, and when?
  • Transcript

    • 1. REGULATION OF GENE EXPRESSION
    • 2. Promoter sequences from 10 bacteriophage and bacterial genes
    • 3. RNA Polymerase Transcribing a Prokaryotic Gene • • • Initiation occurs at a transcription start site in a promoter (DNA sequence) Termination occurs at a transcription stop site Activation of bacterial RNA polymerase requires binding of sigma factor
    • 4. Elongation NTPs
    • 5. TERMINATION • RNA polymerase meets the terminator • Terminator sequence: AAUAAA • RNA polymerase releases from DNA • Prokaryotes-releases at termination signal • Eukaryotes-releases 10-35 base pairs after termination signal
    • 6. Eukaryotic vs. Prokaryotic Transcription • In eukaryotes, transcription and translation occur in separate compartments. • In bacteria, mRNA is polycistronic; in eukaryotes, mRNA is usually monocistronic. – Polycistronic: one mRNA codes for more than one polypeptide – moncistronic: one mRNA codes for only one polypeptide • 3 RNA polymerases in euk., 1 in prok. • Binding of Basal Transcription Factors required for euk. RNA Pol II binding. • “Processing” of mRNA in eukaryotes, no processing in prokaryotes
    • 7. The Lac Operon
    • 8. Glucose effect: no response to inducers in the presence of glucose
    • 9. NEGATIVE REGULATION REPRESSIBLE TRANSCRIPTION THE trp OPERON Aporepressor Operator Co-repressor Active repressor X
    • 10. Different types of negative and positive control of transcription
    • 11. 1 2 3 4 1 2 3 4
    • 12. Transcription in Eukaryotes Eukaryotic RNA Polymerases • Three different RNA polymerases transcribe nuclear genes • Other RNA polymerases found in mitochondria and chloroplasts
    • 13. Transcription control elements in eukaryotes
    • 14. Methylation of CpG islands can block transcription • Direct blocking of TFIID binding Methyl group absent Methyl group present
    • 15. • Genes in eukaryotes vs prokaryotes Have different structures and regulatory signals – Eukaryotic genomes • Are packaged in chromatin and sequestered in a nucleus • Are larger and have multiple chromosomes • Contain mostly non-protein coding DNA (98-99%)
    • 16. DNA is embedded in chromatin
    • 17. Genomes Organism Estimated size (in bases) Estimated gene # Average gene density/base Diploid chromosome # Human 2.9 x 109 ~30,000 1/100,000 46 Rat 2.8 x 109 ~30,000 1/100,000 42 Mouse 2.5 x 109 ~30,000 1/100,000 40 Drosophila 1.8 x 108 13,600 1/9,000 8 Arabidopsis 1.2 x 108 25,500 1/4,000 10 C. elegans 9.7 x 107 19,100 1/5,000 12 S. cerevisiae 1.2 x 107 6,300 1/2,000 32 E. coli 4.7 x 106 3,200 1/1400 1 H. influenzae 1.8 x 106 1,700 1/1000 1 http://www.ornl.gov
    • 18. Recruitment of histone deacteylases methylation of CpG islands promotes silencing
    • 19. As zonas descondensadas de um cromossoma variam ao longo do desenvolvimento do organismo A transcrição ocorre preferencialmente na cromatina menos compactada
    • 20. Gene expression
    • 21. Comparison of Gene Structures

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