Eukaryotic Gene Expression

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Eukaryotic Gene Expression

• Why is gene regulation more complex in eukaryotes
  than prokaryotes?
• Eukaryotes have larger more complex genome
• Eukaryotic DNA must be more highly organized than
  prokaryotic DNA

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Prokaryotic vs. Eukaryotic DNA

• Prokaryotic DNA
• circular
• smaller than eukaryotic DNA
• associated with very few proteins
• less structured and folded

• Eukaryotic DNA
• associated with lots of histone proteins to form
  chromatin fiber
• very extended and tangled during interphase
• condensed into discrete chromosomes during mitosis

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Eukaryotic Development

• Cellular differentiation is the specialization of
  cells during development
• Since all cells have the same DNA, how can
  differentiation occur?
• Gene regulation.

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Selective Gene Expression

• How do cells become specialized?
• Different genes are activated at different times
  during development.
• Each cell utilizes only about 3 of genome

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DNA PackingHelps regulate gene expression

• DNA in one human cells 46 chromosomes would be 3
  meters long.
• How, then, does it all fit into the nucleus?
• DNA packing
• Why do densely packed regions of chromosomes
  inactivate gene expression?
• RNA pol cant get to the gene for transcription.

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• What is the difference between heterochromatin
  and euchromatin?
• Heterochromatin remains highly condensed even
  during interphase
• Barr bodies are X chromosomes condensed into
  heterochromatin
• Telomeres, centromeres also heterochromatin
• euchromatin is chromatin that is not condensed
  and can be transcribed

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Control of Gene Expression

• What are the steps from chromosome to functional
  protein?
• Unpacking ?Transcription? mRNA processing ?
  export from the nucleus ? translation ? protein
  modification
• ANY of these steps can be regulated in eukaryotes

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Chromatin modification

• DNA methylation the addition of methyl groups to
  DNA
• essential for inactivation of the DNA
• Inactive genes in a cell are methylated
• Epigenetic memory due to methylating enzymes that
  methylate the new daughter strand the same as the
  parent strand.
• Can be passed on in repro
• Histone acetylation is the attachment of an
  acetyl group to histone proteins
• acetylation increases likelihood for
  transcription of the DNA

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Transcriptional Control

• Transcription factors allow RNA pol to find the
  promoter region
• association between transcriptional factors and
  enhancer or promoter region regulates gene
  expression

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Posttranscriptional control

• Regulation of RNA processing
• Regulation of mRNA degradation
• Can last from hours to weeks
• Regulation of translation
• initiation sequence can be blocked