1. Cell Division Binary Fission, Mitosis & Meiosis

2. Binary Fission Most cells reproduce through some sort of Cell Division
Prokaryotic cells divide through a simple form of division called Binary Fission
3 step process
Single “naked” strand splits and forms a duplicate of itself.
The two copies move to opposite sides of the cell
Cell “pinches” into two new and identical cells called "daughter cells". (Cell wall then forms if applicable)

3. Mitosis Eukaryotes divide by a more complicated system called Mitosis
This is because:
They have a nucleus which must be broken up and then reformed
They have their DNA “packaged” in the form of Chromosomes
Chromosomes are composed of Chromatin
Made of DNA Strands & Proteins
Also contain Nucleosomes containing Histones - Proteins the DNA is wrapped around Name for the DNA/Protein complex is Chromatin
They usually have more than 1 chromosome (Humans have 23 pairs)
They have numerous organelles to equally share

4. Chromatin / Chromosomes

5. The Cell Cycle
Most of the cell's life is spent doing its regular function.
Cells divide along a rough time frame called its Cell Cycle.
The Cell cycle consists of the folowing steps:
G1 (Gap 1) Phase - Cell performs its normal function (cells which do not divide stay in this stage for their entire life span)
S (Synthesis) Phase - Here the cell actively duplicates its DNA in preparation for division
G2 (Gap 2) Phase - Amount of cytoplasm (including organelles) increases in preparation for division.
Mitosis - Actual division occurs

6. Interphase
Cell Replicates its DNA/Chromosomes in preparation of upcoming division
Animal Cell
Plant cell

7. Mitosis is a continuum of changes.
For description, mitosis is usually broken into five subphases:
prophase,
prometaphase,
metaphase,
anaphase, and
telophase.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

8. By late interphase, the chromosomes have been duplicated but are loosely packed.
The centrosomes have been duplicated and begin to organize microtubules into an aster (“star”).
Fig. 12.5a
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

9. The nucleoli disappear.
In prophase, the chromosomes are tightly coiled, with sister chromatids joined together.
The nucleoli disappear.
The mitotic spindle begins to form and appears to push the centrosomes away from each other toward opposite ends (poles) of the cell.
Fig. 12.5b
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

10. During prometaphase, the nuclear envelope fragments and microtubules from the spindle interact with the chromosomes.
Microtubules from one pole attach to one of two kinetochores, special regions of the centromere, while microtubules from the other pole attach to the other kinetochore.
Fig. 12.5c
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

11. The spindle fibers push the sister chromatids until they are all arranged at the metaphase plate, an imaginary plane equidistant between the poles, defining metaphase.
Fig. 12.5d
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

12. At anaphase, the centromeres divide, separating the sister chromatids.
Each is now pulled toward the pole to which it is attached by spindle fibers.
By the end, the two poles have equivalent collections of chromosomes.
Fig. 12.5e
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

13. Chromatin becomes less tightly coiled.
At telophase, the cell continues to elongate as free spindle fibers from each centrosome push off each other.
Two nuclei begin to form, surrounded by the fragments of the parent’s nuclear envelope.
Chromatin becomes less tightly coiled.
Cytokinesis, division of the cytoplasm, begins.
Fig. 12.5f
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

14. Fig left
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

15. Fig right
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

16. Prophase 1.Chromosomes Shorten and become visible.
2. Centrioles move to opposite sides of the cell
3. Nuclear envelope disappears
4. Spindle Fibers & Astral Fibers both together are known as the Spindle Apparatus begin to form
Animal Cell
Plant Cell

17. Metaphase
Chromosomes line up along center of cell called the Metaphase Plate
Chromosomes attach to spindle fibers
Spindle & Astral fibers are now clearly visible
Animal Cell
Plant Cell

18. Anaphase Centromeres break up separating chromosome copies
Chromosomes are pulled apart to opposite sides of cell
Spindle & Astral fibers begin to break down
Animal Cell
Plant Cell

19. Telophase (cytokenesis)
Nuclear envelope forms around both sets of chromosomes
DNA uncoils
Spindle & Astral fibers completely disappear
Cytokenesis happens with most (but not all) cells
Cytoplasm & organelles move (mostly equally) to either side of the cell.Cell Membrane “pinches” to form 2 separate cells
Animal Cell
Plant
Cell

20. Animal Cytokeneisis
Cytokenesis differs significantly between Animal & Plant cells.
With animals, the membranes pinch together to form a Cleavage Furrow, which eventually fuses to form two daughter cells

21. Plant Cytokenesis
With Plants, a cell wall must be formed between the 2 daughter cells.
Vessicles containing Cellulose form and fuse between the two daughter cells, eventually forming a complete cell wall.

22. Overview of Mitosis

23. Fig. 12.9
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings