1. The Cell Cycle

2. Why Do Cells Divide? Reproduce single celled organisms Repair
Replace old cells
Growth
we all start out as a single cell…

3. Before Division… DNA must condense. How chromosomes form:
Loose DNA = Chromatin
Condensed DNA = Chromosome
How chromosomes form:
DNA wraps around proteins (histones), this continues to coil until condensed.
DNA double helix
DNA and histones
Chromatin
Supercoiled DNA

4. Chromosome Structure Chromatid = One half of a duplicated chromosome.
centromere
Chromatid = One half of a duplicated chromosome.
Sister chromatids are held together at the centromere.

5. 3 Stages of the Cell Cycle
Interphase
Mitosis
Cytokinesis
Did you know…Cell division may be as fast as 30 minutes (in some bacteria) or never (muscle, fat, nerve cells)

6. Interphase Longest phase of the cell cycle. DNA is uncoiled. 3 stages:
Gap 1 (G1): cell growth, organelles replicate
Synthesis (S): DNA is copied
Gap 2 (G2): additional growth (prepare for mitosis)

7. Mitosis Division of the nucleus Has 4 stages
Prophase
Metaphase
Anaphase
Telophase
Produces 2 genetically identical daughter nuclei.
Occurs in somatic cells (all cells except sex cells)

8. Prophase Longest phase of mitosis. Chromosomes condense.
Nuclear membrane dissolves.
Centrioles move to opposite ends of the cell
Spindle fibers form, attach to chromosomes.

9. Metaphase
Chromosomes line up in the center of the cell.

10. Anaphase
Sister chromatids separate, are pulled to opposite ends of the cell.

11. Telophase Spindle fibers disintegrate. Nuclear membrane forms.
Chromosomes begin to uncoil.

12. Cytokinesis Cell pinches apart.
In plant cells, a cell plate forms (will become the cell wall).

13. Cells divide at different rates.
The rate of cell division varies with the needs of the cell.

14. Summary of the Cell Cycle
Cats
Summary of the Cell Cycle
cat

16. Cell Cycle Tutorials
Review:
Crash course:
(shows centrioles and spindle fibers well)
Bozeman Science:

17. Practice Mitosis
(practice, click on mitosis stage matching)