1. Cell Growth and Division
How would you describe the process by which a multicellular organism increases its size?
Why do cells stay small?

2. Objectives Explain the problems that growth causes for cells.
Describe how cell division solves the problems of cell growth.

3. Limits to Cell Growth
The larger a cell becomes, the more demands the cell places on its DNA and the more trouble the cell has moving enough nutrients and wastes across the cell membrane.
Two reasons why cell size is limited:
If a cell were to grow without control, DNA overload would occur.
Rate of material exchange is dependent on surface area

4. Exchanging Materials
Food, oxygen and water enter the cell through the cell membrane. Waste products leave the same way.
The rate at which this exchange takes place depends on surface area (the total area of its cell membrane)

5. Ratio of surface area to volume
As the length of a cell increases, its volume increases faster than its surface area.
The resulting decrease in the cell’s surface-area-to-volume ratio makes it more difficult for the cell to move needed materials in and waste products out.

6. Cell Division
Before a cell becomes too large, it divides into two daughter cells by a process called cell division.

7. What are Chromosomes? Chromosomes are made up of DNA
DNA carries the cell’s genetic code
The cells of every organism have a specific number of chromosomes.

8. Uncoiled DNA

9. DNA Coils into Chromosomes

10. The structure of a chromosome
Chromatin
Chromatid
Centromere
Chromosomes are not visible in most cells except during cell division.
At the beginning of cell division the chromosomes condense into compact, visible structures that can be seen under a light microscope.

11. The Chromosome
Chromosome: “X” shaped cell structure that directs cell activities and passes on traits to new cells.
Each identical strand of the chromosome is called a chromatid.
The strands are held together by a structure called the centromere.
Chromatin: Loosely coiled DNA

12. Parts of a Chromosome

13. The Cell Cycle M Phase Interphase Prophase Metaphase Anaphase
G1 Phase: Cell Growth
S Phase: DNA Replication
G2 Phase: Preparation for Mitosis
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
M Phase

14. I Promised My Aunt Tina Chocolate
The Phases
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
I Promised My Aunt Tina Chocolate

15. Links http://www.cellsalive.com/mitosis.htm

16. Interphase: G1
Cell Grows
Synthesis of proteins and new organelles

17. S-Phase
Chromosomes are duplicated and the synthesis of DNA molecules takes place.

18. G2 Phase
Many of the organelles and molecules required for cell division are produced.
The cell is then ready to enter M-Phase to begin the process of Cell division

19. Prophase The chromatin condense into chromosomes.
The centrioles separate and a spindle begins to form.
The nuclear membrane breaks down.

20. Metaphase The chromosomes line up along the middle of the cell.
“M”eet in the “M”iddle!
Each chromosome is connected to a spindle fiber at its centromere.

21. Anaphase Anaphase pulled Apart
The sister chromatids separate into individual chromosomes and move apart.
Anaphase pulled Apart

22. Telophase Two new Nuclei
The chromosomes gather at opposite ends of the cell and lose their distinct shapes.
Two new nuclear membranes form
Two new Nuclei

23. Cytokinesis The cell membrane pinches the cytoplasm in half.
Each daughter cell has an identical set of duplicate chromosomes.

24. Plant Cells
Plant cells have a cell plate that forms between the two cells.
The cell wall is too rigid to be pinched apart.

25. Length of the Cell Cycle of a Human Liver Cell
Interphase: 21 hours
Growth : 9 hours
DNA Replication: 10 hours
Preparation for Division: 2 hours
Mitosis: 1 hour
Prophase
Metaphase
Anaphase
Telophase

27. Uncontrolled Cell Growth
Cancer- a disorder in which some of the body’s own cells lose the ability to control growth.
Disease of the cell cycle

28. Summary Video