1. Section 8.2 Summary – pages 201 - 210 Cells divide to make a new identical cell. Warm Up: According to the cell theory, where do all cells come from?

2. Section 8.2 Summary – pages 201 - 210 At this moment, cells in your body are growing, dividing, and dying. Old cells are shedding and being replaced. Cuts and bruises are healing Your intestines are producing millions of new cells each second.

3. Section 8.2 Summary – pages 201 - 210 Early biologists noticed that just before cells divide, several short structures suddenly appeared in the nucleus. Then they noticed that after cellular division that these structures would vanish.

4. Section 8.2 Summary – pages 201 - 210 For most of a cell’s life, DNA exists in long strands called chromatin. WAIT TO ANSWER: Where is DNA found in a eukaryotic cell? Nucleus

5. Section 8.2 Summary – pages 201 - 210 Before a cell divides, chromatin coils up into tightly packed structures called chromosomes. CELL REPRODUCTION

6. Chromosome

7. Section 8.2 Summary – pages 201 - 210 Chromosomes are the carriers of genetic material that is copied and passed from generation to generation of cells. CELL REPRODUCTION

8. Section 8.2 Summary – pages 201 - 210 Before a cell can divide- a copy of all the chromosomes needs to be made so that the new “daughter” cell has the exact DNA as the “parent” cell. CELL REPRODUCTION “Parent Cell” Chromosomes “Daughter Cell” Chromosomes

9. Chapter Assessment Why does a cell make a copy of it’s chromosomes before it divides and makes another cell? TALK TO YOUR NEIGHBOR: (I will randomly call on someone in a few seconds)

10. Section 8.2 Summary – pages 201 - 210 When mitosis is complete, unicellular organisms remain as single cells. Result of Mitosis

11. Section 8.2 Summary – pages 201 - 210 Following mitosis, in multi-cellular organisms, cell growth and reproduction result in groups of cells that work together as tissue to perform a specific function. Result of Mitosis

12. Section 8.2 Summary – pages 201 - 210 The cell cycle is the sequence of growth and division of a cell. (life cycle) The cell cycle consists of Interphase, Mitosis, and Cytokinesis The Cell Cycle

13. 13 Eukaryotic Cell Cycle The eukaryotic cell cycle has 5 main phases: 1.G 1 2.S (synthesis) 3. G 2 4. M (mitosis) 5. C (cytokinesis) The length of a complete cell cycle varies greatly among cell types. interphase

14. Section 8.2 Summary – pages 201 - 210 The majority of a cell’s life is spent in the growth period known as interphase. The Cell Cycle

15. 15 Interphase Interphase is composed of: G 1 – time of cell GROWTH S phase – SYNTHESIS of DNA (DNA replication) - 2 sister chromatids are produced G 2 – more GROWTH - chromosomes condense

16. 16 Interphase Following S phase, the sister chromatids appear to share a centromere. In fact, the centromere has been replicated but the 2 centromeres are held together by cohesin proteins. Proteins are attached to the centromere. Microtubules attach to the kinetochore.

17. 17 Chromatid Kinetochore microtubules Centromere region of chromosome Metaphase chromosome Cohesin proteins Kinetochore Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

18. 18 Interphase During G 2 the chromosomes undergo condensation, becoming tightly coiled. Centrioles (microtubule-organizing centers) replicate and one centriole moves to each pole.

19. Prophase 1 st step in Mitosis Mitosis begins (cell begins to divide) Nucleolus disappears. Centrioles (or poles) appear and begin to move to opposite end of the cell. Spindle fibers form between the poles. Centrioles Sister chromatids Spindle fibers

20. Prophase Animal Cell Plant Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Spindle fibers Centrioles

21. Metaphase 2 nd step in Mitosis Chromatids (or pairs of chromosomes) attach to the spindle fibers – line up at the equator (along the metaphase plate). Centrioles Spindle fibers

22. Metaphase Animal Cell Plant Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

23. Anaphase 3 rd step in Mitosis Sister Chromatids (or pairs of chromosomes) separate at the centromere (kinetichore)and begin to move to opposite poles of the cell. Centrioles Spindle fibers

24. Anaphase Animal Cell Plant Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

25. Telophase 4th s tep in Mitosis Chromatids reach their poles Two new nuclei form. Chromosomes appear as chromatin (threads rather than rods). Spindle Fibers disappears & cleavage furrow forms Nuclei Chromat in

26. Telophase Animal Cell Plant Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

27. Cytokinesis occurs after mitosis Cell membrane moves inward to create two daughter cells – each with its own nucleus with identical chromosomes.

28. Animal Mitosis -- Review Interphase Prophase Metaphase Anaphase Telophase Interphase

29. Plant Mitosis -- Review Interphase Prophase Metaphase Anaphase Telophase Interphase

30. The cell cycle is controlled by both internal and external signals. A signal is a molecule that either stimulates or inhibits a metabolic event. Growth factors are external signals received at the plasma membrane. Cell Cycle Checkpoints There appear to be three checkpoints where the cell cycle either stops or continues onward, depending on the internal signals it receives. A special protein must be present for the cell to move from the G 1 stage to the S stage, and from the G 2 stage to the M stage. The cell cycle stops at the G 2 stage if DNA has not finished replicating; stopping the cell cycle at this stage allows time for repair of possible damaged DNA. Also, the cycle stops if chromosomes are not distributed accurately to daughter cells. DNA damage also stops the cycle at the G 1 checkpoint if apoptosis is triggered Control of the Cell Cycle

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32. Section 8.3 Summary – pages 211 - 213 Scientists believe that if something goes wrong with these enzymes, they cause cells to skip a long interphase and divide a lot faster than they should. Control of Cell Cycle There are enzymes (proteins) that control the rate of the cell’s life cycle.

33. Section 8.3 Summary – pages 211 - 213 Cancer is a growth resulting from uncontrolled cell division. Occasionally, cells lose control of the cell cycle. Control of Cell Cycle This loss of control may be caused by environmental factors or certain inheritances.

34. Section 8.2 Summary – pages 201 - 210 During Interphase, under a microscope, there doesn’t appear to be much going on. BUT, Interphase is the busiest phase of the cell cycle During this time the cell is growing, making more organelles, and chromatin (DNA) is replicating. The Cell Cycle Interphase Chromatin Replicated Chromatin