II. Mitosis and Cytokinesis A. DNA

1. DNA - deoxyribose nucleic acid  a. double stranded helix b. organic molecule  c. monomers are nucleotides 6 billion/cell  d. stores genetic informatiom  e. pass on instructions through genetic code  f. copies itself in S phase

2. Chromosomes  a. contain genes  1. unit of heredity  b. codes for proteins  1. that carry out cellular functions  2. give genetic traits

3. Chromosome Structure  a. rod shaped,  b. tightly coiled  c. wrapped around histones (protein) during cell division  1. histones-maintain shape of chromosome

4. Chromatin  a. threadlike strands of DNA in the nucleus until the start of prophase.  b. chromatid is one half a chromosome  c. there are 2 identical chromatids/chromosome  d. centromere - holds chromatids together during metaphase  e. telomeres protect the ends from unraveling.

E. Purpose of Mitosis  1. Growth  2. Repair injured cells  3. Replace dead cells  4. pass on the code

2. Mitosis (10%) - nuclear division   a. Prophase   1. DNA coils & thickens to form chromosomes   2. nucleolus and nuclear membrane disintegrates   3. 2 pairs of centrosomes w/centrioles appear at the poles

  a. centrosomes produce spindle fibers   b. asters radiate from centrosomes   c. polar fibers cross entire cell, centrosome to centrosome   d. kinetochore fibers attach to centromere of chromatid

  b. Metaphase   1. spindle fibers move chromosomes to equator   2. chromosomes line up across middle of cell from their sister chromatid

  c. Anaphase   1. chromatids separate, centromere divides   2. move to opposite poles by spindle fibers

  d. Telophase   1. chromosomes at opposite poles   2. spindle fibers & centrioles disappear   3. chromosomes uncoil into chromatin   4. nuclear envelop form around each new set of chromotin   5. nucleolus forms   6. if animal cell - cleavage furrow develops (pinch in half)

  6. Cytokinesis (10%)   a. equal division of cytoplasm   b. begins during telophase   c. two new identical cells (daughter cells)   d. equal in size, number of organelles   e. new nucleus   f. identical copies of chromosomes   g. cleavage furrow continues to divide cell in half   h. plant cell forms cell plate that forms the cell wall