Cell Growth and Division

1. Cell Growth and Division

2. Cell division is needed to… • Grow – most organisms grow by producing more cells • Repair wounds and damaged cells • Develop and change

3. Why do cells divide?(aka, why are cells small?) • Two main reasons why cells can’t grow indefinitely: • A larger cell places more demands on its DNA (more things to control and not enough DNA) • Surface-to-volume ratio decreases as size increases • Thus, before the cell becomes too large, it divides

4. When do cells divide (or stop)? • When cells crowd each other, they stop dividing • When internal factors signal the cell to start or stop dividing • e.g., p53 gene makes sure the cell doesn’t divide until chromosomes have doubled; cyclin enzymes start/stop the cell cycle • When external chemical or physical signals (growth regulators) stimulate or inhibit growth and division (Cancer is an example of uncontrolled cell growth….we will discuss cancer later in the unit)

5. Cells divide at different rates • The rate of cell division varies with the need for the type of cell…

6. What is the cell cycle? • The series of phases that cells go through as they grow and divide. • A continuous process, but we divide it into 3 stages: • Interphase • Mitosis • Cytokinesis http://images1.clinicaltools.com/images/gene/celldivision/cellcycle.jpg

7. Stage 1: Interphase • Cell life between divisions • The longest stage! • Nucleus is still present • Phases: • Gap 0 (G0) – grows and functions • Gap 1 (G1)– duplicates organelles and molecules needed for cell division • Synthesis (S) – duplicates DNA (in chromotin form) • Gap 2 (G2 ) – checks for errors

8. Stage 2: Mitosis • Duplication and division of the cell nucleus • Phases: • Prophase • Metaphase • Anaphase • Telophase

9. Stage 3: Cytokinesis • Pinching off of the cytoplasm • (Often grouped as part of mitosis) Mitosis + cytokinesis result in two identical daughter cells! YouTube: Mitosis

10. Now!, Let’s look at your Mitosis Flipbook and compare…

11. (Review…) Interphase • Nucleus is still intact and the nucleolus is visible. • DNA is in chromatin form • Includes G1, S, and G2

12. Mitosis step 1: Prophase • Centrioles separate and produce spindle fibers • Chromatin condenses to form chromosomes • Nuclear envelope and nucleolus break down prophase → pro (#1!)

13. Chromatin? Chromosomes? Chromatin= DNA unwound (looks like spaghetti) Chromosome= DNA condensed and organized; looks like this: 2 chromosomes Sister chromatids= a duplicated chromosome Centromere = the place where chromotids are connected Some useful DNA vocabulary!

14. To recap… During prophase, chromatin condense into chromosomes… which have duplicated into sister chromatids, attached to each other at their centromeres.

15. Mitosis step 1: Prophase • Centrioles separate and produce spindle fibers • Chromatin condenses to form chromosomes • Nuclear envelope and nucleolus break down prophase → pro (#1!)

16. Mitosis step 2: Metaphase • Chromosomes line up at the middle of the cell • A spindle fiber attaches to each sister chromatid at the centromere metaphase → middle

17. Mitosis step 3: Anaphase • Spindle fibers contract and pull apart the chromosomes to opposite ends of the cell anaphase → apart

18. Mitosis step 4: Telophase • Chromosomes return to chromatin form • Nuclear membranes and nucleolus reform • Spindle fibers disappear • Nuclear division is complete telophase → telephone

19. After mitosis…Stage 3: Cytokinesis • Pinching of the cytoplasm, resulting in two identical daughter cells. The cell cycle: IPMATC I Passed My Algebra Test with a “C” YouTube: Mitosis Video Mitosis Review

20. Mitosis in plants • Plants don’t have centrioles • Cell plate forms during telophase • During cytokinesis, cell plate separates the daughter cells and becomes the new cell wall Blood lily mitosis

21. Mitosis in real cells…PMAT

22. Where doesn’t mitosis happen? • Nerve and blood cells are different • Sex cells (gametes) undergo a different division process

23. Your summary…