1. MITOSIS!!!!!!!! Cell Growth and Division

2. Limits to Cell Growth As the cell becomes larger, there are more demands placed on the cell. It can cause a DNA overload. The overload of DNA happens because as a cell increases in size, it doesn’t make extra copies of DNA. If the cell was to continue to grow, it would run into an information crisis. The DNA would not be able to support the cell!

3. Limits to Cell Growth It can also cause a problem with exchanging material. If a cell grows too large, it is more difficult to get oxygen and nutrients.

4. Mitosis and Unicellular Organisms Mitosis in single celled organisms helps to make new individuals. This is asexual reproduction. Ex – Paramecia and Amoeba

5. Mitosis and Multicellular Organisms Mitosis in multicellular organisms helps with growth and repair. Ex- plants and animal cells.

6. Cell Division Growing cells divide into 2 daughter cells DNA must be copied first Mitosis – division of the nucleus Cytokinesis – division of the cytoplasm

7. Overview of Mitosis There are three major processes to mitosis Replication of genetic material Separation of genetic material Formation of two daughter cells

8. The Nucleus and Cell Division Changes have to happen here before mitosis DNA has to be copied to be passed on In nondividing cells = Chromosomes are not visible because the DNA and proteins are spread throughout the nucleus Chromatin – the DNA as a mass of thin twisted threads DNA is wrapped around histones (proteins)

9. The Nucleus and Cell Division In dividing cells = Chromatin shortens and thickens forming chromosomes Can be seen Before cell division the chromosome has to be copied. When the chromosomes are copied, there are two sister chromatids made. The chromatids are attached in the middle at the centromere.

11. The Cell Cycle Are the events a cell goes through as it grows and divides. A cell grows, prepares for division and divides to form two daughter cells, each of which will begin the cell cycle again.

12. includes is divided into Concept Map Section 10-2 Cell Cycle M phase (Mitosis) Interphase G 1 phaseS phaseProphaseG 2 phaseMetaphaseTelophaseAnaphase

13. Interphase Can be very long G 1 phase – cells grow, increase in size and make new organelles and proteins S phase – chromosomes are replicated G 2 phase – shortest phase; organelles and molecules are made

14. Mitosis Divided into phase – Prophase Metaphase Anaphase Telophase

15. M phase G 2 phase S phase G 1 phase Section 10-2

16. Prophase Longest phase of mitosis Takes up about 50-60% of time Chromosomes are visible Centrioles move to opposite sides of the nucleus Centrioles are in the centrosome region which helps to organize the spindle Spindle – fanlike microtubule structure that helps separate the chromosomes

17. Prophase Chromosomes become attached to fibers in the spindle at a point near the centromere of each chromatid Plant cells don’t have centrioles but still organize their spindles At the end of prophase, the chromosomes are soiled tightly, nucleolus disappears, and the nuclear envelope breaks down.

18. Metaphase Chromosomes line up at the center of the cell

19. Anaphase Centromeres that join the sister chromatids split The sister chromatids become separated and now again have individual chromosomes for each cell

20. Telophase Chromosomes disperse into a tangle of dense material Nuclear envelope returns Spindle breaks apart Nucleolus is again visible

21. Cytokinesis The cytoplasm divides to form the two cells Usually happens at the same time as telophase In animals – the cell membrane is pulled inward and is pinched In plants – a cell plate forms and then the cell wall replaces it

24. Control of Cell Division The cell cycle can be turned on and off Cyclin – protein that regulates the cell cycle Amount increases during cell division Regulate timing of cell cycle Internal regulators Proteins that respond to events inside the cell Allows to proceed only when the inside of the cell is ready For example, the chromosomes are copied

25. A sample of cytoplasm is removed from a cell in mitosis. The sample is injected into a second cell in G 2 of interphase. As a result, the second cell enters mitosis. Figure 10–8 Effect of Cyclins Section 10-3

26. Control of Cell Division External regulators Proteins that respond to events outside of the cell Tells the division to speed up or slow down Growth factors Molecules on neighboring cells cause the cycle to slow down or stop

27. Uncontrolled Cell Growth Cancer – body’s own cells lose the ability to control growth Don’t respond to signals that regulate the growth of most cells Cells divide uncontrollably and form tumors which can affect tissues Cancer cells can break loose and spread throughout the body Control over the cycle is broken

28. Uncontrolled Cell Growth Cancer cont’d The cells don’t respond to external or internal regulators Scientists found lots of cancer cells with a defect in the gene p53 which normally stops the cell cycle until all chromosomes have been properly replicated.