1. Chapter 9 Cellular Reproduction
Mitosis
And
The Cell Cycle

2. Cellular Growth
Cells grow until they reach their size limit, then they either stop growing or divide.
Cell size is limited.
Most cells are less than 100 micrometers in diameter (smaller than the period at the end of the sentence in your book)

3. Cell Size Limitation Ratio of surface area to volume
Area covered by the plasma membrane
Volume – space taken by the inner contents of the cell (organelles, cytoplasm, nucleus)
To calculate ratio: multiply length x width x height of cell
The larger the cell, the less efficient it is
Small cells have a higher ratio of surface area to volume and can sustain themselves more easily.

4. Why does a high ratio of surface area to volume benefit a cell?
Easier to transport substances
As cell grows, its volume increases much more rapidly than the surface area making it difficult for the cell to supply nutrients and to expel waste products.
The smaller the cell, the more efficient it is
Cells remain small to maximize the ability of diffusion and motor proteins to transport nutrients and waste products.

5. Cellular Communication
The need for signaling proteins to move throughout the cell limits cell size
If cell becomes too large, it becomes almost impossible for cellular communications
i.e., the signals that trigger protein synthesis might not reach the ribosome fast enough for protein synthesis to occur to sustain the cell

6. The Cell Cycle
Once a cell reaches its size limit – either it will stop growing or it will divide
Most cells divide
Prevents cell from getting too large
Allows for cell to reproduce
Allows for growth
Allows injuries to heal
Cell grows and divides – The Cell Cycle –
One complete cycle produces two cells from each original cell – provides continuous production of new cells

7. The Cell Cycle Three main stages
Interphase – cell growth, cell functions, copies DNA
3 stages
Gap 1 – cell growth and normal functions
Synthesis – DNA is replicated
Gap 2 – cell prepares for Mitosis
Mitosis – cell’s nucleus and nuclear material divide
4 stages
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis – cytoplasm divides, creating new cells

8. Synthesis stage of Interphase
Involves:
Chromosomes – structures that contain genetic material of cell – passed on from generation to generation
Chromatin: relaxed form of DNA in cell’s nucleus

9. Prokaryotic Cell Division
Reproduce by a method called binary fission.
Eukaryotes use the method known as the Cell Cycle.

10. The Cell Cycle

11. Mitosis

12. Phases of Mitosis (PMAT)
Interphase-prior to mitosis
Mitosis:
Prophase
Metaphase
Anaphase
Telophase

13. Interphase
Cell grows
Carries out normal cell processes
DNA replicates

14. Prophase Nuclear membrane disintegrates Nucleolus disappears
Chromosomes condense
Spindle apparatus begins to form between poles

15. Metaphase
Chromosomes attach to spindle fibers and align along equator of cell

16. Anaphase
Microtubules shorten, moving chromosomes to opposite poles

17. Telophase Chromosomes reach poles of cell Nuclear envelope re-forms
Nucleolus reappears
Chromosomes decondense

18. Cytokinesis In plant cells: Cell plate forms Dividing daughter cells
In animal cells:
*Cleavage furrow forms at equator of cell and pinches inward until cell divides in two

19. Cell Cycle Regulation
The normal cell cycle is regulated by cyclin proteins.
The timing and rate of cell division are important to the health of an organism.
Rate varies depending on type of cell.
Role of cyclins: cyclins bind to enzymes called cyclin-dependent kinases (CDKs) in the stages of the cell cyle

20. Cell Cycle Regulation
Different cyclin/CDK combinations control different activities at different stages in the cell cycle.
Figure 9.11 on page 253 (know when cyclins/CDK become active)
In G1 stage of interphase , the combination of cyclin and CDK signals the start of the cell cycle.
Different cyclin/CDK combinations signal other activities (DNA replication, protein synthesis, and nuclear division)
The same cyclin/CDK combination also signals the end of the cell cycle.

21. Cell Cycle Regulation Quality control checkpoints
A checkpoint near the end of the G1 stage monitors for DNA damage and can stop the cycle before entering the S stage of interphase
Spindle checkpoints also in place – if a failure of the spindle fibers is detected, the cycle can be stopped before cytokinesis.
Note checkpoints on figure 9.11

22. Abnormal Cell Cycle: Cancer
Although there are checkpoints in cell cycle, the process sometimes fails.
Cancer is the uncontrolled cell growth and division of cells – a failure in the regulation of the cell cycle.
Cancer cells can kill an organism by crowding out normal cells, resulting in the loss of tissue function.
Cancer cells spend less time in interphase than normal cells, can grow and divide unrestrained as long as they are supplied with essential nutrients.

23. Cancer
Causes – mutations or changes in the segments of DNA that control the production of proteins
Repair system of these changes fail
Environmental factors can affect the occurrence as well – carcinogens: substances and agents known to cause cancer

24. Cancer Avoiding carcinogens can reduce the risk of cancer.
FDA works to make sure that what you eat and drink are safe
Known carcinogens – asbestos, tobacco, radiation
Ways to protect yourself –sunscreen, don’t smoke or use tobacco, etc.

25. Cancer
Cancer genetics – chance of cancer increases with age due to changes in DNA
Inheriting risk increases chances of getting cancer

26. Apoptosis Not every cell is destined to survive
Some cells go through a process called apoptosis – programmed cell death
Shrink and shrivel in a controlled process
All animal cells appear to have apoptosis
Example – human hands and feet – prevents webbing
Example – plants – loss of leaves
Also occurs in cells that are damaged beyond repair- protecting organisms from developing cancerous growths

27. Stem Cells Most cells are designed for specialized function
Stem cells are unspecialized cells that can develop into specialized cells when under the right conditions

28. Stem Cells
Two basic types
Embryonic stem cells
Adult stem cells

29. Embryonic Stem Cells
Once a sperm fertilizes the egg, the resulting mass of cells divides repeatedly until there are about 100 – 150 cells.
Not specialized yet – embryonic stem cells
If separated, each of these has the capability of developing into a wide variety of specialized cells
Controversial because of ethical concerns

30. Adult Stem Cells Found in various tissues in the body
Might be used to maintain and repair the same kind of tissue in which they are found
A newborn has adult stem cells
Might be able to develop into different kinds of cells, providing new treatments for many diseases and conditions
Less controversial because the adult stem cells can be obtained with the consent of their donors

31. Treatment Using Adult Stem Cells
In 1999, researchers at Harvard Medical School used nervous system stem cells to restore lost brain tissue in mice
In 2000, a team of researchers at the University of Florida used pancreatic stem cells to restore pancreas function in a mouse with diabetes