1. Mitosis and the Cell Cycle
Cell reproduction

2. Some Definitions Somatic Cells – body cells
Produced through mitosis
Has 46 chromosomes (23 pairs)
Homolog – each member of a chromosome pair
Diploid (2n) – total of 46 chromosomes in people – zygote & somatic cells
Haploid (n) – total of 23 chromosomes in people, gametes (sperm & egg)

4. The Cell Cycle
The sequence of growth and division of a cell.
95% of cell cycle in interphase
5% of cell cycle in mitosis

5. Cell Cycle 4 phases of the cell cycle G1 Phase includes a G0 S Phase
M Phase (Mitosis and Cytokinesis happens during this phase)

6. Interphase Growth Stage 1 (G1) – metabolic activity of the cell
G0 is a resting phase
Synthesis Stage (S) – metabolic activity of the cell, replication of DNA
Growth Stage 2 (G2) – metabolic activity of the cell, prepare for division

8. Checkpoint control system
Checkpoints
cell cycle controlled by STOP & GO chemical signals at critical points
signals indicate if key cellular processes have been completed correctly

9. Cancer and the Cell Cycle
Cancer is a disease that occurs when the cell cycle is no longer regulated. This may happen because a cell’s DNA becomes damaged. Damage can occur due to exposure to hazards such as radiation or toxic chemicals. Cancerous cells generally divide much faster than normal cells. They may form a mass of abnormal cells called a tumor.

10. Frequency of cell division
Frequency of cell division varies by cell type
embryo
cell cycle < 20 minute
skin cells
divide frequently throughout life
12-24 hours cycle
liver cells
retain ability to divide, but keep it in reserve
divide once every year or two
mature nerve cells & muscle cells
do not divide at all after maturity
permanently in G0

11. Anatomy of a Chromosome
Sister chromatids
One original and one copy from the S phase
Centromere
Center where sister chromatids attach

12. Mitosis
Happens in all cells except sex cells (gametes) which is a different process.
Nuclear Division (division of the nucleus)
4 major stages

13. 1st Stage - Prophase Nuclear envelope disappears
Chromosomes condense – can see sister chromatids and centromere
Spindle forms
Centrioles go to poles

14. 2nd Stage - Metaphase Chromosomes move to the equator of spindle
Each chromatid is attached to spindle with centromere

15. 3rd Stage - Anaphase Centromeres split
Sister chromatids are pulled apart to opposite poles of the cell
Each chromatid is now a separate chromosome

16. 4th Stage - Telophase Nuclear envelopes (2) reform
Chromosomes begin to uncoil
Cleavage furrow forms

17. After Telophase Mitosis is complete; cell division is not!!!
NOTE:
After Telophase Mitosis is complete; cell division is not!!!

18. Cytokinesis Division of the Cytoplasm
Two new daughter cells are now separate (both identical to the original parent cell)
When cytokinesis is complete; cell division is complete.