1. The Cell Cycle
Ch. 10

2. CELL CYCLE
Life cycle of cells
2 Stages
Interphase
Cell Division

4. Importance of Cell Division
According to the cell theory, new cells can only arise from existing cells.
There are several cases when new cells are needed, such as:

5. 1) Reproduction
For single celled organisms, like prokaryotes (bacteria), cell division is used for reproduction.
Asexual

6. 2) Growth For multicellular organisms, cell division allows growth.
We all started as one cell, but we needed many new cells.

7. 3) Cell Replacement As cells age, they wear out and die.
New cells are needed to replace them.

8. 4) Repairing Wounds
If a multicellular organism is injured, the damaged cells need to be replaced.

9. Stage 1 & 2 of the Cell Cycle

10. Interphase – 1st stage

11. After new cells are formed, they need time to grow and prepare for another round of cell division – this is Interphase.

12. Stages of Interphase G1 S G2

13. G1 phase
Gap 1
Cell growth
Increases in size and makes new proteins and organelles.

14. S phase
Synthesis
DNA replication

15. G2 phase
Gap 2
Prepare to divide
make more organelles

16. Cell Division – 2nd Stage

17. Period during which cells replicate and divide.
Consists of Mitosis and Cytokinesis
Called the M phase.

18. Mitosis

20. Mitosis The process that copies the nucleus
Results in one cell with two identical nuclei

21. 4 Stages of Mitosis
Prophase
Metaphase
Anaphase
Telophase

22. P M A T
Matt
Mitosis

23. PROPHASE
Chromatin condenses to chromosomes.
Nucleolus disappears.
Nuclear membrane breaks down.

26. METAPHASE
Chromosomes line up in the middle of the cell

29. ANAPHASE
Sister chromatids are pulled apart.

32. TELOPHASE
Chromosomes return to chromatin.
Two identical nuclei form.
Nucleolus reappears.
Nuclear membrane reforms.

35. Cytokinesis

36. Cytokinesis Process that divides the cytoplasm and the organelles
Results in two genetically identical daughter cells (each with one nucleus)

37. In cells without cell walls
The cell membrane pinches in half forming two separate cells.

38. In cells with cell walls
A new piece of cell wall must be formed to separate the two new cells.

39. Controlling the cell cycle
Cell division is carefully controlled by:
The P53 gene
Cyclins (special proteins)
Cell-to-cell contact

40. When cells go wild!!!
If cells do not stop dividing when they get the signal to, they become cancerous
Often caused by a defect in the P53 gene

41. Cancer Cells Divide uncontrollably Live much longer than normal cells
Crowd out healthy cells, allowing the cancer to spread
Are difficult to treat because they are YOUR cells – they just don’t listen to your body anymore