Chromatin in a developing salamander ovum

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Chromatin in a developing salamander ovum
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Eukaryote genomes (Chap 14)
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• LOTS of DNA in eukaryotesmostly non-coding
• Repetitive elements 59
• Introns regulatory elements, other noncoding
  DNA 39
• Structural genesonly 1.5 of DNA

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Repetitive DNA 59 of genome

• Satellite DNA micro (1-3 bp) mini (10-40 bp)
  tandem repeats (includes telomeres, centromeres)
• Transposon related (SINEs LINEs) including Alu
  elements
• Moderately repetitive DNA (large sequences,
  including genes for ribosomes, tRNAs)
• Pseudogenes

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Alu elements (10-11 of genome)

• a very abundant class of short interspersed
  repetitive DNA, similar to the gene for RNA of
  the signal recognition particle that binds
  ribosomes to ER
• 300 bp over over...11 of human genome
• Naming cut by restriction enzyme Alu-1
  Arthrobacter luteus.
• Significance as genetic markers in forensics,
  phylogenetics

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Retrotransposons
How did human genome end up with 1.5 million Alu
elements? Genetic elements are replicated and
moved by retrotransposition. Retrotransposons
(copy and paste transposons) are similar to
retroviruses
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Retrotransposon movement
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Repetitive DNA (59)

• Simple sequence (satellite) DNA (3)
• Multiple, tandem copies of short sequences
• Why satellite? AT vs GC density
• Telomeres centromeres
• Significance in forensics, phylogenetics

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Gene duplication gene families

• Many protein coding genes have also undergone
  replication in genome
• Pseudogenes- recognizably homologous with
  functional genes but not transcribed.
• multigene families, e.g. globin gene families.
• The genome is an untidy scene, littered with
  clues to evolutionary history

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The evolution of human ?-globin and ?-globin gene
families
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What about the coding genes? (1.5)
Functions of protein-coding genes in
Drosophila (sums to 80) 13,449 genes 18,941
mRNAs
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Gene expression in multicellular eukaryotes

• Variety of cell types
• All have same genome
• Which genes get expressed when
• Roles development, cell differentiation,metabo
  lic regulation

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Control of gene expression

• Chromatin modifications
• DNA methylation
• Histone acetylation
• Control of transcription
• Alternative splicing
• Degradation of mRNA
• Blockage of translation

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A eukaryotic gene with its control elements and
transcript
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2. Control of Transcription (Fig. 14.14)

• Control elements (DNA)
• Enhancer and silencer sequences
• Transcription factors (bind DNA)
• activators and repressors
• Coordinate control of genes via similar control
  elements, rather than operons

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A model for enhancer action
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Control of gene expression, continued

• 3) Alternative RNA splicing (editing)

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Control of gene expression, continued

• Degradation of mRNA
• Blockage of translation
• siRNA and miRNA

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Control of gene expression, continued
Post-translation

• 6) Protein processing, transport
• 7) Control of enzyme activity by effectors and
  inhibitors
• 8) Proteasomes degrade ubiquitin-tagged proteins

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Degradation of a protein by a proteasome
Ubiquitin protein tags other proteins for
destruction by proteasomes
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Proteasomes