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Eukaryotic Gene Expression

Eukaryotic Gene Expression. The “More Complex” Genome. genome characteristics differ dramatically Table 14.1. E. coli and yeast, the “eukaryotic E. coli” Table 14.2. Table 14.3. Table 14.4. The Eukaryotic Genome. prokaryotic and eukaryotic genomes encode many of the same functions

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Eukaryotic Gene Expression

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  1. Eukaryotic Gene Expression The “More Complex” Genome

  2. genome characteristics differ dramaticallyTable 14.1

  3. E. coli and yeast, the “eukaryotic E. coli”Table 14.2

  4. Table 14.3

  5. Table 14.4

  6. The Eukaryotic Genome • prokaryotic and eukaryotic genomes encode many of the same functions • eukaryotes encode additional functions associated with organelles • genomes of multicellular eukaryotes encode additional functions • each eukaryotic kingdom encodes specialized products • so, eukaryotic genomes are larger • but why so much?

  7. Genomes Vary in Size

  8. Table 14.5

  9. The Eukaryotic Genome • Genomics • analyzes and compares entire genomes of different organisms • sequences of many genomes are complete • Proteomics • analyzes and compares the functions of the proteins in an cells, tissues, organs, organisms

  10. The Eukaryotic Genome • repetitive DNA sequences • highly repetitive sequences (103 - 106 each) • tandemly repeated satellites (5-50 bp) • mainly at centromeres • minisatellites (12-100 bp) • Variable Number Tandem Repeats • microsatellites (1-5 bp x 10-50) • small, scattered clusters • untranslated

  11. Figure 11.18

  12. rRNA genes are tandemly repeatedFigure 14.2

  13. The Eukaryotic Genome • repetitive DNA sequences • moderately repetitive sequences • telomeres (~2500 x TTAGGG per chromosome end - human) • clustered tRNA, rRNA genes (~280 rRNA coding units on 5 chromosomes - human) • transposable elements (transposons)

  14. The Eukaryotic Genome • transposable elements (transposons) • SINES: transcribed elements ~500 bp long • LINES: elements ~7000 bp long; some are expressed • >100,000 copies • retrotransposition • retrotransposons: like retroviral genomes • DNA transposons: translocating DNAs

  15. Figure 14.3

  16. gene expression in eukaryotesFigure 14.1

  17. The Eukaryotic Genome • Gene expression • protein-coding genes • contain non-coding sequences • promoter • terminator • introns interrupt the coding sequence found in exons • the primary transcript is processed to produce an mRNA

  18. eukaryotic genes contain non-coding regionsFigure 14.4

  19. Figure 14.5

  20. DNA-mRNA hybrids revealedthe presence of intronsFigure 14.6

  21. the ends of primary transcripts are processedFigure 14.9 capping tailing

  22. The Eukaryotic Genome • Gene expression • protein-coding genes • primary transcripts are processed to produce mRNAs primary transcripts are processed to produce mRNAs • the 5’ end is capped with reversed GTP • the 3’ end is given a “poly (A)” tail at the polyadenylation site, AAUAAA • introns are removed during splicing by snRNPs of the spliceosome

  23. introns are removed from primary transcripts byspliceosomesFigure 14.10

  24. regulation of eukaryotic gene expression may occur at many different pointsFigure 14.11

  25. transcriptionfactorsassist RNA polymerase to bind to the promoterFigure 14.12

  26. The Eukaryotic Genome • expression of eukaryotic genes is highly regulated • three different RNA polymerases transcribe different classes of genes • each RNA polymerase binds to a different class of promoters • RNA polymerases require transcription factors in order to bind to their promoters • transcriptional activators may bind far from the promoter

  27. DNA elements are binding sites for proteins of the transcription machineryFigure 14.13

  28. DNA looping can bring distant protein factors into contact with the promoter complexFigure 14.13

  29. The Eukaryotic Genome • expression of eukaryotic genes is highly regulated • eukaryotes do not group genes with related functions together in operons • genes that are coordinately expressed share DNA elements that bind the same transcriptional regulator proteins

  30. common response elements enable coordinated expression of independentgenesFigure 14.14

  31. gene regulators bind to DNA elements • common motifs are found among gene regulators Figure 14.15

  32. The Eukaryotic Genome • many genes are present in single copies • some genes are present in a few similar copies in “gene families” • one or more expressed, functional genes • non-functional pseudogenes

  33. human globin genes are found in two gene familiesFigure 14.7 nonfunctional pseudogenes

  34. changes in expression of alternate globin genesFigure 14.8

  35. transcription factors remodel chromatin to bind promotersFigure 14.16

  36. The Eukaryotic Genome • DNA is packaged as chromatin in the nucleus • transcription factors remodel chromatin to bind promoters • condensed DNA can “turn off” entire regions of chromosomes

  37. The Eukaryotic Genome • one gene can encode more than one polypeptide • some primary transcripts undergo alternative splicing

  38. alternate splicing: multiple polypeptides from single genesFigure 14.20

  39. The Eukaryotic Genome • proteins are ultimately removed, degraded and replaced • the proteasome degrades proteins that are tagged for degradation

  40. the proteasome recognizes ubiquitin-bound polypeptidesFigure 14.22

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