1. The Cell Cycle
Mitosis …

2. THINK:
Of how many cells are you composed?
When an organism grows bigger do you get more cells or just bigger cells or both?
When do your cells divide the fastest? Slowest?
Do cells ever stop dividing?
Are all cells capable of division and replacement?

3. Why does a cell divide?
As a cell absorbs nutrients and gets larger, the volume of the cell increases faster than the surface area.
-Therefore, the demands of the cell (the volume) exceed the ability of the cell to bring in nutrients and export wastes. Solution? Divide into two smaller cells

4. When is cell division occurring?
GROWTH -increase number of cells
REPAIR -replace lost cells due to injury, disease
CANCER – Abnormally high rates of cell division due to mutation
Different kinds of cells divide at different rates:
E. coli – 20 minutes
Yeast cell – 2 hours
Amoeba – a few days
Human embryo cell – minutes
Human adult cell – 8 hours to 100 days

5. How long is one cell cycle. Depends on the type of cell. Ex
How long is one cell cycle? Depends on the type of cell. Ex. Skin cells every 24 hours. Some bacteria every 2 hours. Some cells every 3 months. Nerve cells, never. Cancer cells very short.
Programmed cell death: Each cell type will only do so many cell cycles then die. (Apoptosis)

6. Aging
All cells die after a certain number of divisions (programmed cell death-”apoptosis”). At any given time some cells are dividing and some cells are dying.
Childhood Cell division > cell death
Adulthood Cell division = cell death
Aging Cell division < cell death

7. Control of the Cell Cycle Cell proliferation

8. Interphase ~ 90% of the time.
Ø   G1: Little new cell absorbs nutrients and grows larger. Does protein synthesis, its job.
Ø   S phase: Synthesis of new DNA (DNA replication) for daughter cells in preparation for mitosis.
Ø   G2: Cell continues to grow, do protein synthesis, do its job. Gets too large, needs to divide.

9. What do chromosomes look like?
Chromosomes exist in 2 different states, before and after they replicate their DNA.
Before replication, chromosomes have one chromatid. After replication, chromosomes have 2 sister chromatids, held together at the centromere.
Each chromatid is one piece of DNA with its supporting proteins.

10. Remember that diploid cells have two copies of each chromosome, one from each parent. These pairs of chromosomes are NOT attached together.

11. Structure of a eukaryotic chromosome
unreplicated chromosome
arm
centromere

12. Prior to cell division: chromosomes (DNA) are replicated (duplicated)
duplicated chromosome
– attached at their centromeres
– while attached, known as
sister chromatids
duplicated
chromosome

13. daughter
chromosomes
sister
chromatids

14. MITOSIS
Equal division of the 2 sets of DNA amongst the 2 daughter cells.
4 Stages: “PMAT”
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
How the Cell Cycle Works
Mitosis Animation
Cell Cycle

15. What is Mitotic Cell Division?
Division of somatic cells (body cells)
(non reproductive cells) in
eukaryotic organisms
A single cell divides into two
identical daughter cells
(cellular reproduction)
=> Maintains chromosome ploidy of cell

16. Ploidy – refers to the number of pairs of
chromosomes in cells
haploid – one copy of each
chromosome
– designated as “n”
diploid – two copies (= pair) of each
chromosome
– designated as “2n”

17. As a cell enters mitosis from interphase it has 2 complete sets of chromosomes because of replication in the S phase.
Each set must be re-arranged and distributed into the 2 new daughter nuclei. This is mitosis.

18. Prophase…
-Chromatin condenses (coils) into chromosomes. Sister chromatids joined by centromere.
-Nuclear membrane dissolves.
-Centrioles divide and move to opposite poles forming spindle between them.

19. chromatin
nucleolus
nucleus
centrioles
condensing
chromosomes

20. Metaphase -Centromeres lock on to spindle fiber
-Sister chromatids line up on metaphase plate.
-Centromeres lock on to spindle fiber

21. Anaphase
-Centromeres divide.
-Spindle fibere contract pulling sister chromatids apart to poles.

22. Telophase: -New nuclear membranes form around new nuclei
Mitosis Movie

23. CYTO KINESIS – cytoplasm divides Cytoplasm splits into 2 cells.
-Animal cells: Cleavage furrow forms from outside in. -
Plant cells: Division/cell plate forms from inside out.

24. Cell now returns to interphase
Cell now returns to interphase . The chromosomes uncoil back into chromatin. The whole cell cycle starts over again…..
Control of the Cell Cycle

25. At any point in time the cells in a tissue will be at different stages in the cell cycle.

27. Mitosis Stages
Put these in the correct order..

28. The Guarantee of Mitosis…
The 2 daughter cells formed are identical to each other and identical to the mother cell.
Why is this so important?
Mitosis The Movie

29. Mitosis is asexual
In Mitosis, each daughter cell is exactly the same as the original mother cell.
Cell Differentiation

30. Propogation of plants by cuttings
Budding of Yeast
These are other examples of the uses of mitosis to create new organisms asexually:
Propogation of plants by cuttings
Runners from plants like strawberries

31. Resources Mitosis Dance Mitosis  CANCER
How Cancer grows
Mitosis:
Cell Cycle & Cancer Animations:
Cell Biology & Cancer Animations:
Mitosis & Meiosis Interactive Exercise:
Mitosis Animations:
Plant Cell Mitosis:
Mitosis Dance
Meiosis Square Dance