Chapter 10

1. Chapter 10 Cell Growth & Division 1

2. 10 –1 Cell Growth • Which has larger cells: an adult elephant or a baby elephant? • Neither! They are the same size. The adult just has more cells. 2

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4. Two main reasons why cells divide rather than continuing to grow indefinitely: • The larger a cell becomes, the more demands the cell places on its DNA. DNA "Overload" • A huge cell needs a lot of DNA, but cells only have one set of DNA. • The cell has more trouble moving enough nutrients and wastes across the cell membrane. • it would be more difficult to get sufficient amounts of oxygen and nutrients in and waste products out • Cells don’t get bigger… Organisms do!! 4

5. Division of the Cell • Cell divides into 2 new daughter cells. • DNA duplication occurs before division (own genetic set) • Each daughter cell has increased surface area to volume, which allows exchange of materials with the environment. 5

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7. 10–2 Cell Division • Every cell must first copy its genetic information before cell division begins. • Each daughter cell then gets a complete copy of that information. • Eukaryotes are more complex than Prokaryotes. In Eukaryotes: • The first stage, division of the cell nucleus, is called mitosis. The second stage, division of the cytoplasm, is called cytokinesis. 7

8. Chromosomes • genetic information is passed on from one generation of cells to the next • Chromosomes – made up of DNA and proteins • every organism has a specific number of chromosomes • fruit flies = 8 chromosomes • humans = 46 chromosomes • carrot = 18 chromosomes • Chicken = 78 chromosomes 8

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11. Chromosomes (cont.) • chromosomes aren’t visible except during cell division…otherwise the DNA and proteins are spread throughout the nucleus. • at the beginning of cell division, chromosomes condense and become visible. • before cell division, each chromosome is duplicated. 11

12. Parts of the Chromosome • chromatids – sister chromatids: each chromosome consists of 2 identical sister chromatids. (separated during cell division) • centromere – where each pair of chromatids is attached near center (protein disk) • entering cell division in humans = 46 chromosomes each with sister chromatids. 12

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14. The Cell Cycle • recurring events in the life of the cell. • the series of events that cells go through as they grow and divide • During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells, each of which then begins the cycle again. 14

15. The Cell Cycle 15

16. 4 Phases of the Cell Cycle G1 S  G2  M • G1 = intense growth and activity • S = DNA replication • G2 = intense growth and activity [Interphase = G1,S, G2 ] • M = Mitosis (nucleus division) and cytokinesis (cytoplasm division) 16

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18. The Cell Cycle Animation • http://www.cellsalive.com/cell_cycle.htm 18

19. Events of the Cell Cycle • G1 = cells do most of their growing. • During this phase, cells increase in size and synthesize new proteins and organelles. • S = DNA is replicated • synthesis of DNA molecules • Key proteins associated with the chromosomes are also synthesized • G2 = shortest phase of interphase • organelles and proteins required for cell division are produced 19

20. Mitosis • 4 phases: [P M A T] • Prophase • Metaphase • Anaphase • Telophase • Lasts from a few minutes to several days 20

22. Prophase  • longest phase of mitosis (50 to 60 percent of the total time of Mitosis) • chromosomes become visible • centrioles separate – go to opposite ends of the cell • centrioles lie in a region called the centrosome that helps to organize the spindle • condensed chromosomes become attached to fibers in the spindle at a point near the centromere of each chromatid 22

23. Prophase (cont.) • nucleolus disappears (breaks up) • nuclear envelope breaks down • chromosomes coil more tightly 23

24. Early prophase Late prophase Mid prophase 24

25. Metaphase  • lasts only a few minutes • the chromosomes line up across the center of the cell • Microtubules connect the centromere of each chromosome to the two poles of the spindle 25

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27. Anaphase  • the centromeres split • sister chromatids separate  become individual chromosomes • chromosomes continue until they have separated into two groups near the poles of the spindle • Anaphase ends when the chromosomes stop moving 27

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29. Telophase  • Chromosomes begin to uncoil into a tangle of dense material (chromatin) • A nuclear envelope re-forms around each cluster of chromosomes • The spindle begins to break apart • A nucleolus becomes visible in each daughter nucleus 29

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34. Mitosis Animation • http://www.cellsalive.com/mitosis.htm 34

35. Cytokinesis • two nuclei — each with a duplicate set of chromosomes — are formed, within the cytoplasm of a single cell • the division of the cytoplasm itself • occurs at the same time as telophase 35

36. animal cells = cell membrane is drawn inward until the cytoplasm is pinched into two nearly equal parts • plants = the cell plate forms midway between the divided nuclei • The cell plate gradually develops into a separating membrane. • A cell wall then begins to appear in the cell plate. 36

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39. 10-3 Regulating the Cell Cycle • Controls on Cell Division • When cells come into contact with each other, cells respond by stopping growth • when space is put between cells, cells begin growing once again. • controls on cell growth can be turned on and off 39

40. Contact Inhibition 40

41. Cell Cycle Regulators • Cyclins (proteins) regulate the timing of the cell cycle in eukaryotic cells. • two types of regulatory proteins: those that occur inside the cell and those that occur outside the cell. 41

42. 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 • For example, several regulatory proteins make sure that a cell does not enter mitosis until all its chromosomes have been replicated. • Another regulatory protein prevents a cell from entering anaphase until all its chromosomes are attached to the mitotic spindle. 42

43. External Regulators  • Proteins that respond to events outside the cell • direct cells to speed up or slow down the cell cycle. • Growth factors are among the most important external regulators. They stimulate the growth and division of cells. Growth regulators are especially important during embryonic development and wound healing. 43

44. Uncontrolled Cell Growth • cells that divide uncontrollably and form masses are called tumors • Cancer cells do not respond to the signals that regulate the growth of most cells and may break loose from tumors and spread throughout the body (cancer) • Metastasis = is the spread of cancer from its primary site to other places in the body 44

45. Causes of cancer • smoking tobacco • radiation exposure • even viral infection 45

46. Why does cancer occur? • Many (but not all) cancers have a defect in a gene called p53 • p53 normally halts the cell cycle until all chromosomes have been properly replicated • Damaged or defective p53 genes cause the cells to lose the information needed to respond to signals that would normally control their growth 46

47. Mitosis Animation • http://www.cellsalive.com/mitosis.htm 47

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