Eukaryotic Gene Expression by ppc90937

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									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
• 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?
              Genomes Vary in Size
Organism         Genome Size (bp)         Genes
  E. coli                4,460,000 (h)              4,300
   Yeast                   24,136,000               6,200
Nematode                   97,000,000              19,099
 Fruit fly                180,000,000              13,600
Puffer fish               365,000,000             ~30,000
  Human                 6,200,000,000              22,000
Arabidopsis               119,000,000     15,000 (26,000)
   Rice                   389,000,000              37,544
   Lily               600,000,000,000    ??????????????
Table 14.5
         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
         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
Figure 11.18
rRNA genes are tandemly repeated
         Figure 14.2
        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)
         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
Figure 14.3
   gene
expression
    in
eukaryotes
Figure 14.1
         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
eukaryotic genes contain non-coding regions
                Figure 14.4
Figure 14.5
DNA-mRNA
   hybrids
  revealed
     the
  presence
      of
   introns
 Figure 14.6
the ends of primary transcripts
        are processed
          Figure 14.9




capping                  tailing
         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
   introns
      are
  removed
     from
   primary
 transcripts
      by
spliceosomes
Figure 14.10
  regulation
       of
  eukaryotic
gene expression
  may occur
   at many
   different
    points
 Figure 14.11
 transcription
    factors
     assist
RNA polymerase
    to bind
     to the
   promoter
 Figure 14.12
         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
  DNA elements are binding sites for
proteins of the transcription machinery
              Figure 14.13
DNA looping can bring distant protein factors
  into contact with the promoter complex
                Figure 14.13
         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
common response
elements enable
coordinated
expression of
independent
genes
Figure 14.14
gene regulators bind to DNA elements
• common motifs are found among gene
  regulators
             Figure 14.15
         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
human globin genes are found in
      two gene families
         Figure 14.7




      nonfunctional pseudogenes
changes in expression of
 alternate globin genes
       Figure 14.8
transcription
factors
remodel
chromatin
to bind
promoters
Figure 14.16
         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
         The Eukaryotic Genome
• one gene can encode more than one
  polypeptide
   – some primary transcripts undergo
     alternative splicing
alternate splicing: multiple polypeptides from
                  single genes
                 Figure 14.20
         The Eukaryotic Genome
• proteins are ultimately removed, degraded and
  replaced
   – the proteasome degrades proteins that are
     tagged for degradation
 the proteasome recognizes
ubiquitin-bound polypeptides
        Figure 14.22

								
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