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