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Eukaryotic Gene Control. Gene Organization: . Chromatin: Complex of DNA and Proteins Structure base on DNA packing. DNA Packing:. Histones: positively charged amino acids Five types (H1, H2A, H2B, H3,H4) DNA- negatively charged phosphate groups. DNA Packing: .

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gene organization
Gene Organization:
  • Chromatin:
    • Complex of DNA and Proteins
    • Structure base on DNA packing
dna packing
DNA Packing:
  • Histones: positively charged amino acids
    • Five types (H1, H2A, H2B, H3,H4)
  • DNA- negatively charged phosphate groups
dna packing1
DNA Packing:
  • Nucleosomes: “beads on a string”
    • Basic unit
    • DNA wound around two molecules composed of histones (H2 – H4)
      • H1 = histone tail
    • 10nm
higher level of dna packing
Higher Level of DNA Packing:
  • Coiling of 10nm = 30nm chromatin fiber
  • Looped domain = 30nm chromatin fiber attaches to chromosome scaffold = 300nm fiber
  • Metaphase chromosome- maximal compaction
    • 1400 nm
heterochromatin
Heterochromatin:
  • Highly condensed interphase DNA
    • Can not be transcribed
euchromatin
Euchromatin:
  • Less compacted interphase DNA
    • Can be transcribed
differential gene expression on many levels
Differential gene expression on many levels:
  • 1. Pre Transcription
    • Chromatin
  • 2. Transcription
  • 2. Post Transcription
    • RNA processing, transport to cytoplasm, degradation of mRNA
  • 3. Translation
  • 4. Post Translation
    • Cleavage and chemical modification, degradation of protein
examples pre transcription
Examples: Pre-transcription
  • Histone Acetylation of chromatin:
    • Histones = group of 5 proteins associated with the coiling of DNA (positively charged regions)
    • Histone acetylation: acetyl group (-COCH3
      • Attached to positively charged regions
      • Neutralizes the histones
      • Causes DNA to become loser
      • Transcription proteins can access the DNA with greater ease
slide12

Deacetylation (removing of acetyl groups) creates a tighter, super coiled DNA structure

    • Difficult for transcription to proceed
dna methylation and demethylation
DNA methylation and demethylation:
  • Inactive Mammalian X chromosomes (Barr bodies):
    • Highly methylated (-CH3) bases, particularly cytosine
    • Removing of methyl groups can activate these genes
gene regulation gone wrong
Gene regulation gone wrong:
  • Proto- oncogenes:
    • Normal cellular genes
    • Code for proteins that stimulate normal cell growth and division
  • Oncogenes:
    • Cancer causing genes
how do proto oncogenes become oncogenes
How do proto-oncogenes become oncogenes?
  • Movement of DNA- translocation
  • Amplification:
  • Point mutations:
tumor suppressor genes
Tumor- Suppressor genes
  • Genes that inhibit cell division
  • Mutation of these genes may stimulate uncontrollable cell growth
normal cell signaling interference
Normal Cell Signaling Interference:
  • Interference with a cell signal pathway
    • 1. can stimulate pathways of the cell cycle to promote uncontrollable cell division
    • 2. can inhibit cell cycle pathways that prevent suppression of cell division allowing uncontrolled cell division