Mitosis

1. Mitosis “My”tosis Pages 246-248

2. mitosis M-Phase

3. Mitosis • There are 4 main phases of mitosis • Prophase • Metaphase • Anaphase • Telophase • Depending on the organism, each phase can last anywhere from a few minutes to several days!

4. Prophase The cell prior to Prophase (interphase) • The 1st and longest phase of mitosis • Takes 50% - 60% of mitosis’ total time • The chromatin condenses into visible chromosomes • The nuclear envelope breaks down • Prophase “prepares”

5. Prophase 1. The centrioles move to opposite sides of the nucleus • Tiny structures in the cytoplasm which produce spindle fibers 2. Spindle fibers form from the centrioles • Fanlike microtubule structure that acts to separate the chromosomes The end of prophase moving into metaphase

6. Metaphase • The 2nd phase of mitosis • Often lasts only a few minutes 1. The chromosomes line up across the middle of the cell 2. The spindle fibers attach to the centromere • Metaphase “Middle”

7. aNAPHASE • The 3rd phase of mitosis 1. The spindle fibers pull at the centromere, separating the sister chromatids 2. Each sister chromatid moves apart toward separate poles of the cell 3. Anaphase is complete when the individual chromosomes stop moving • Anaphase “Away”

8. Telophase • The 4th and final phase of mitosis 1. The condensed chromosomes begin to reform back to chromatin 2. The nuclear envelope begins to reform around the chromosomes • Telophase “Two”

9. Cytokinesis • At the end of telophase, mitosis is complete and we are left with 2 new nuclei • Cytokinesis is the division of the cell’s cytoplasm • Is the completion of the M phase • Cytokinesis usually takes place at the same time as telophase • As a result we have 2 new “daughter” cells which are identical to the “parent” cell

10. Video • Video #1 • Mitosis Rap • Cell cycle and growth

11. Reflect

12. Review • 1. What are the 6 stagesof the cell division? • 2. What are the 4 main stagesof mitosis? • 3. What is/are the major characteristic(s) of prophase? • 4. What is/are the major characteristic(s) of metaphase? • 5. What is/are the major characteristic(s) of anaphase?

13. Review • 6. What is/are the major characteristic(s) of telophase? • 7. What is/are the major characteristic(s) of cytokinesis? • 8. What do we get as a result of mitosis? • 9. Would this be a good way to reproduce as a species?

14. Regulating the Cell Cycle To be or to be and be and be and be and be and be and be and be……….. Pages 250-252

15. Reflect

16. Regulating the cell cycle • Cell growth and cell division must be carefully controlled • Different cells of the body divide at different rates • Nervous and muscles cells rarely divide once formed • Cells of skin, digestive tract and marrow divide often • Newly divided cells make it possible to replace old cells that are worn out or break down

17. Controls on cell division • Within the laboratory we can look at cell growth • Cells tend to stop growing when they come into contact with other cells • When cells are removed, growth will start again

18. Controls on cell division • In our bodies we can see the same event • When there is an injury such as a cut, cells at the edge are stimulated to divide • New cells are produced and healing begins • By the end of the healing process, cells stop dividing

19. Cell cycle regulators • Scientists wanted to know what tells cells to divide • Performed experiments on dividing cells and noticed level of protein cyclin rose and fell with progression of cell cycle • Cyclin – regulates the cell cycle • Caused spindle formation when placed in non-dividing cells • Cyclins – family of proteins that regulate the timing of the cell cycle • Two types of regulatory proteins

20. Types of regulatory proteins 1. Internal Regulators – proteins that respond to events inside the cell • Allow the cell cycle to proceed only when certain processes have happened inside the cell • Makes sure the cell doesn’t enter mitosis until all chromosomes have been replicated

21. Types of regulatory proteins 2. External Regulators – proteins that respond to events outside the cell • Direct the cell to speed up or slow down the cell cycle • Growth Factors – tell the cell when to grow and/or divide • Especially important in embryonic development and wound healing • Molecules on Neighboring Cells – cause cells to slow down growth or stop their cycle • Prevents excessive cell growth or tissues interrupting others

22. review • True or false, all cells divide at the same rate? • Do skin cells divide often or rarely? • Do brain cells divide often or rarely? • When cells grow to reach other cells they continue dividing, true or false? • What regulates the cell cycle?

23. review • Where are they made? (Hint: think about last unit) • Cyclin is an example of an internal regulator, true or false? • What is an example of an external regulator? • What would happen if a mutation occurred that changed the mRNA sequence that produces the protein cyclin so that UGA became UGG? (Thinker)

24. Uncontrolled Cell Growth • The consequences of uncontrolled cell growth can be severe on an organism • Cancer – disorder where cells do not respond to the bodies signal to regulate cell growth • As a result, cells divide uncontrollably and form masses called tumors • Cancer cells can break loose from tumors and spread throughout the body=metastasis

25. What causes loss of control? • Control has broken down for some reason… • Cells no longer respond to internal or external regulators • Exposure • Tobacco • Radiation • Viral infections • Genetic Defect • P53 gene – supposed to halt cell cycle no longer functions