Cell Divison and Mitosis

Why are cells small?

1. Exchange of waste and nutrients is more efficient

2. DNA can’t keep up with cell demands for info

   1. Ideal cell:  

      • large surface area

      • small volume

      • (large SA/V ratio)

Why do cells divide?

• Growth (of multicellular organisms)

• Repair (replacing cells in injury)

• Reproduction 

  • sexual 

  • asexual (cell division, budding, splitting, cutting)

    • aka cloning (genetically identical)

Chromosomes

• DNA —> Chromatin —> Chromosomes —> Sister Chromatids

• A single package of  DNA, the number of chromosomes depends on the species

  • Adders Tongue Fern 1260, Dog 78, Chimpanzee 48, Human 46

Cell Cycle

• From birth to reproduction of a cell

• speed depends on type of cell 

       (fast in skin vs. slow in lung cells)

• 2 phases

1. Interphase - cell is doing its job, preparing to divide

   1. G1:

   2. S:

   3. G2

2. Mitotic phase - nucleus and cell divide

   1. mitosis (nucleus divides)

   2. cytokinesis (cell divides)

Mitotic Phase

• Results in 2 identical daughter cells

  • 2 parts

    • Mitosis - nucleus and chromosomes divide

      1. interphase

      2. prophase

      3. metaphase

      4. anaphase

      5. telophase

      6. cytokinesis

    • Cytokinesis - cytoplasm divides

Prophase

• chromosomes become visible (coil up)

• nuclear envelope breaks up

• spindle forms from centrioles.

  • spindle:  microtubules that guide chromosomes during mitosis

Metaphase

• chromosomes line up across the cell

• spindle connects to sister chromatids at centromere

Anaphase

• sister chromatids get pulled apart 

  • spindle fibers pull chromosomes toward opposite ends of the cell

Telophase - reverse of prophase

• spindle disappears

• nuclear envelopes reform around each nucleus

• chromosomes uncoil

Cytokinesis

• splitting of the cytoplasm

• animals: plasma membrane pinches in

• plants:  a cell plate forms in between the cells and grows out to sever the 2 cells

Mitosis