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

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…