1. Mitosis:
The Great Divide

2. Why Would a Cell Divide?
As cells absorb nutrients and get larger, a large demand is placed on the cell’s DNA & the volume of the cell increases faster than the surface area
Surface area for exchange not great enough to support cell’s needs
This means that a cell has difficulties with
1. absorbing enough nutrients
2. getting rid of waste fast enough
So what’s a cell to do? divide in 2!

3. When Would a Cell Divide?
Growth of the organism
Repair of slightly damaged cells
Replacement of cells
Different cells divide at different rates:
Most mammalian cells = hours
Some bacterial cells = minutes

4. Getting Older… How does cell division change over a lifetime?
All cells are only allowed to complete a certain number of divisions
Then they experience apoptosis (programmed cell death or self destruction)
How does cell division change over a lifetime?
Childhood = cell division > cell death
Adulthood = cell division = cell death
The Later Years = cell division < cell death

5. The Cell Cycle vs Mitosis
The Cell cycle includes all the steps required for an entire cell to divide (Interphase, Mitosis and Cytokinesis)
Mitosis includes the steps that are carried out for only the nucleus to divide (Prophase, Metaphase, Anaphase and Telophase)

6. The Cell Cycle

7. Two Stages of the Cell Cycle
2 stages = Interphase-growth & replication of DNA & Mitotic phase (Mitosis & Cytokinesis)-division of cell into 2 daughter cells
Cell spends about 90% of the time in interphase!
Thanks to person who introduced me
Explain presentation style
Different, wacky, interactive
Reason for madness- will be reviewed during implications
May be asked to be an active participant
May be asked to reinforce others
Will be reinforced with candy
Comments/questions welcomed throughout
Reinforce me for doing well
Have participants guess the number of new things they will learn today

8. Interphase G1 (1st gap) = cells absorb nutrients, grow & make proteins
Divided into 3 phases:
G1 (1st gap) = cells absorb nutrients, grow & make proteins
S (synthesis) = cells duplicate DNA & continue to grow in preparation for cell division during mitosis
G2 (2nd gap ) = cells keep growing & making proteins & get ready to divide in 2

9. Interphase occurs before mitosis begins
What’s happening??
1. Cells grow
2. DNA/Chromosomes are copied (DNA Replication!)
Chromosomes appear as threadlike coils (chromatin) at the start, but each chromosome and its copy(sister chromosome) change to sister chromatids at end of this phase
3. Preparation for Mitosis
CELL MEMBRANE
Nucleus
Cytoplasm

10. Interphase Plant Cell Animal Cell
Photographs from:

11. Mitosis
Mitosis includes the steps that are carried out for only the nucleus to divide
Mitosis is divided into 4 stages
Prophase
Metaphase
Anaphase
Telophase

12. Prophase 1st step in Mitosis
Mitosis begins (cell begins to divide)
Chromatin condenses and chromosomes become visible
Sister chromatids held together by a centromere
Nuclear membrane dissolves
Centrioles appear and move to opposite end of the cell.
Spindle fibers form between the centrioles.
Centrioles
Sister chromatids
Spindle fibers

13. Prophase Plant Cell Animal Cell Spindle fibers Centrioles
Photographs from:

14. Metaphase 2nd step in Mitosis
Chromosomes line-up along the center of the cell and attach to the spindle fibers at their centromere (center of chromosome)
Centrioles
Spindle fibers

15. Metaphase Plant Cell Animal Cell
Photographs from:

16. Anaphase 3rd step in Mitosis
Spindle fibers contract and sister chromatids (pairs of chromosomes) are pulled away from one another towards the poles or opposite ends of the cell.
Centrioles
Spindle fibers

17. Anaphase Plant Cell Animal Cell
Photographs from:

18. Telophase 4th and final step in Mitosis
Nuclear membranes form around the two new nuclei .
Chromosomes appear as chromatin (threads rather than rods).
Mitosis ends.
Nuclear membranes
Nucleus
Nucleus
Chromatin

19. Telophase Plant Cell Animal Cell
Photographs from:

20. Cytokinesis occurs after mitosis
Cell membrane moves inward to create two identical daughter cells – each with its own nucleus containing identical chromosomes.
The cytoplasm is distributed equally between the two new cells before separation

21. What Mitosis Actually Looks Like
Interphase
Metaphase
Prophase
Telophase
Anaphase

22. Animal Mitosis
Interphase                                                             
Prophase                                                             
Metaphase                                                             
Anaphase                                                             
Telophase                                                             

23. Plant Mitosis
Interphase                                                             
Prophase                                                             
Metaphase                                                             
Anaphase                                                             
Telophase                                                             

24. Summary of Mitosis

25. What Happens After Mitosis?
The cells return to interphase
Chromosomes uncoil back into chromatin
The cycle repeats itself over & over…

26. Mitosis Animation

27. Can You Identify the Stages of Mitosis?
Put the following mitosis stages in the correct sequence