1. Cell Cycle

2. Cell Growth
Why do cells divide?

3. Cells divide for 2 main reasons
As cell grows larger more demands are placed on the cell’s DNA
It also is more difficult for the cell to move enough nutrients and waste across the cell membrane

5. The cell cycle Interphase: Longest part of cell cycle
“in between” cell divisions
Cell prepares to divide
3 stages of Interphase, G1 S, G2

6. During G1
Cell grows, synthesizes new proteins and organelles

7. During S phase
Chromosomes are replicated
Synthesis of DNA molecules

8. G2 Phase Shortest part of Interphase
Organelles and molecules needed for cell division are made
At end, cell ready for “M” phase of cell cycle

9. Mitosis is the “M” phase of the cell cycle
Is the division of the cell nucleus
Made up of 4 stages
Prophase, Metaphase, Anaphase, Telophase

10. Cell Cycle
During the cell cycle a cell grows, prepares for cell division, and divides to form 2 daughter cells, which then begin the cycle again

11. Mitosis: Occurs in nucleus
PROPHASE:
longest phase
Chromosomes become visible
Centrioles move to opposite ends of nucleus
Spindle forms
Nuclear membrane breaks down

13. Metaphase Chromosomes line up in middle of cell
Each chromosome connected to a spindle fiber at its centromere

15. Anaphase Sister chromatids separate into individual chromosomes
Chromosomes move apart to opposite ends of cell

17. Telophase
New nuclear envelope forms around each of the groups of chromosomes
Spindle breaks down

19. Cytokinesis
Cell membrane draws inward and pinches into 2 nearly equal parts

24. Cell Cycle Video
Mitosis.mpg

25. Controls on cell division
Can be internal or external
So cell division can be turned on and off.

26. Internal Regulators
CYCLINS (type of protein) regulate the timing of the cell cycle in eukaryotic cells

27. External regulators Contact with other cells stops growth
Growth factors: Stimulate growth and division in cells. Can be on surface of neighboring cells as well.

28. Uncontrolled cell growth
Cancer arises when some of the body’s own cells lose the ability to control growth.
Cancer cells do not respond to the signals that regulate the growth of most cells
Form masses of cells called tumors