Cell Division


Principles Module 32


  • Detail the differences between division in prokaryotic and eukaryotic cells
  • Define the cellular structures involved in mitosis and cytokinesis
  • Describe the eukaryotic cell cycle and phases of mitosis

Key Points

Bacterial cell division

  • division is different in prokaryotes and eukaryotes by necessity
  • binary fission is simple division in bacteria
    • single circular chromosome replicated at same time as division
    • proteins control partitioning of DNA into daughter cells
    • replication begins at ori site, goes bidirectionally around
    • septum separates the 2 new cells
      • formation is regulated by proteins
      • forms at midpoint of cell, FtsZ protein forms ring

Eukaryotic chromosomes

  • packaging
    • 40% DNA, 60% protein called histones
    • allow for coiling of DNA, packaging to hi density
    • ~ 200 bp = 8 histones = nucleosome
    • nucleosomes wrapped into solenoids, form 30 nm fiber
  • ploidy
    • haploid is the number of chromosomes a species has
      • human haploid # is 23
      • Arabidopsis haploid # is 5
    • many species have 2 versionsof each chromosome, are diploid
      • versions called homologues, encode same genes at same places
      • slight differences in each from parents (alleles)
  • replication
    • results in each chromosome having exact duplicate copy
    • copies held together as sister chromatids

Overview of eukaryotic cell cycle

  • interphase
    • G1 (gap) growth phase, majority of most cells’ cycle
    • S synthesis of exact copy of genome
    • G2 (gap 2) growth, organelle replication, prep for mitosis
  • M (mitosis) separation of 2 daughter genomes
  • cytokinesis partitioning of cytoplasm


  • centromere is a constriction on chromosome
    • made up of repeat sequences of DNA
  • kinetochore a disk shaped collection of proteins attached to centromere
    • microtubules attach here during mitosis
  • centrioles
    • MT organizing centers at poles of cell
  • spindle is MT network that pulls chromosomes apart


  • prophase
    • condensation of chromosomes
    • spindle apparatus forms
    • nuclear envelope disintegrates
  • prometaphase
    • chromosomes attach to spindle at kinetochore
    • congression pulls chromosomes to center of cell
      • recall the growth of MTs by adding and subtracting tubulins
  • metaphase
    • chromosomes aligned at cell equator, called the metaphase plate
  • anaphase
    • centromeres split, sister chromatids separate from each other
    • kinetochores pulled toward poles by removal of tubulins
    • poles move apart
  • telophase
    • spindle breaks down, nuclear envelope reconstitutes
    • chromosomes de-condense


  • cells w/out walls
    • actin forms a belt, constricts to pinch cell, form cleavage furrow
  • cells w/ walls
    • deposits of membrane, new wall carbohydrates in middle, cell plate

In-class Activities

Questions for Practice

  • Compare and contrast prokaryotic and eukaryotic division. What are some reasons why this process should be different?
  • What is the mitotic spindle? What is it made of? When does it form?
  • List and briefly describe each of the major phases of mitosis.