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Prokaryotic Cell Division, Chromosomes

prokaryotic cell division - division by binary fission  

  • genome made of single, circular DNA found in nucleoid area
  • replication of DNA begins at specific site and goes bidirectionally around to specific site of termination
  • cell elongates, DNA gets attached to the membrane
  • septum - new membrane growing near the midpoint during division
    • composed of FtsZ protein ring
  • eukaryotic cells developed mitosis to deal w/ larger, nucleus-enclosed genomes

mitosis - occurs differently in different organisms 

  • protists - 2 ways
    • microtubules (w/ tubulin) pass through nucleus membrane tunnels and sets up axis for division (nucleus remains intact)
    • microtubule spindle forms between centrioles at opposite sides; kinetochore microtubules pull chromosomes to each pole (nucleus remains intact)
  • yeasts - spindle microtubule forms inside nucleus between poles
    • single kinetochore microtubule attaches to chromosomes, pulls them to each end
  • animals - spindle microtubule forms between centrioles outside the nucleus
    • nucleus envelope breaks down
    • kinetochore microtubules attach chromosomes to poles

chromosome - found in cells of all eukaryotes; 40% DNA, 60% protein  

  • most eukaryotes have 10-50 chromosomes (humans have 46, 23 pairs)
  • monosomy - condition where organism lacks a chromosome; won’t survive embryonic development
  • trisomy - extra copy of a chromosome; fatal unless extra copy of very small chromosome (genetic defects still take place)
  • chromatin - DNA/protein complex
    • heterochromatin - chromatin domains not expressed
    • euchromatin - chromatin domains expressed
  • DNA coiled to allow it to fit in smaller space
  • nucleosome - 200 nucleotides coiled around 8 histones
    • solenoid - coils of a string of nucleosomes wrapped together; radially loops around protein scaffold during mitosis
  • histones (positively charged) attract negatively charged phosphate groups in DNA

karyotype - specific chromosome array (different between organisms) 

  • haploid (n) - # of chromosomes needed to define an organism
  • diploid (2n) - 2x haploid number; # of chromosomes in humans, some other species
  • centromere - condensed area found on all eukaryotic chromosomes
  • 2 sister chromatids share common centromere after replication
  • chromosomes counted by # of centromeres
Subject: 
Biology
Subject X2: 
Biology

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