Cell Growth & Division

1. Cell Growth & Division

2. Cellular Reproduction • Organism’s life begins as one cell • Rudolf Virchow (1858) stated: All cells come from cells • Prokaryotes divide only to reproduce • Asexual repro: 1 parent  2 daughters • AKA Binary fission (“dividing in half”) • One set of DNA duplicates, cell divides

3. Eukaryotic cells divide for reproduction, growth, and replacement of cells • Other organisms (plants & animals especially) reproduce through sexual reproduction • Sperm + Egg  offspring • Offspring gets two sets of genetic information, one from each parent

4. 10-1 Cell Growth Limits to cell growth • DNA overload • Exchanging materials • Ratio of surface area to volume

5. 10-1 Cell Growth DNA overload • When a cell is small, its DNA is able to meet all of the cell’s needs. • As the cell grows it produces more organelles, but the DNA is not replicated and it cannot meet the cell’s needs.

6. 10-1 Cell Growth Exchanging materials • The rate at which food and oxygen are used up and waste products are produced depends on the cell’s volume. • As the cell grows it becomes more difficult for it to get rid of wastes and to get food and oxygen into the cell.

7. 10-1 Cell Growth Ratio of surface area to volume • Imagine a cell that is shaped like a cube. • The surface area of a cell would be equal to length x width x number of sides(6) of a cell. • The volume of the cell would be equal to length x width x height of the cell. • The volume of the cell increases more rapidly than the surface area.

8. 10-1 Cell Growth Example Cell size Surface area volume Ratio of surface area to volume

9. 10-1 Cell Growth Division of the cell • The process by which a cell divides into two new daughter cells is called cell division. • Before the cell divides, it replicates all of its DNA. • This process reduces cell volume and solves the DNA overload problem. Division of the cell – Cell growth

10. 10-2 Cell Division The Chromosome • DNA is contained in structures called chromosomes within the nucleus of the cell • “chroma” color, “soma” body • Most of the time, chromatin fills the nucleus • Tangled mass of fibers of DNA & protein • When a cell begins to divide, the chromatin condenses and coils into chromosomes • Each chromosome has one long DNA molecule containing thousands of genes

11. 10-2 Cell Division

12. 10-2 Cell Division The Chromosome • Before a cell divides, it must duplicate its chromosomes • DNA replication! • Once duplicated, the chromosomes have sister chromatids with identical genes, joined at a centromere • When the cell divides, half goes to each daughter cell

13. 10-2 Cell Division

14. 10-2 Cell Division Chromosomes • The information that is passed from one generation to the next is carried by chromosomes. • They are made up of DNA and proteins • A chromosome consists of two sister chromatids.

15. 10-2 Cell Division The Cell Cycle • Sequence of events from the time a cell divides to when it forms two daughter cells • Serves to double the cell’s parts, then splits • Stages: • Interphase 90% • Mitotic phase 10%

16. 10-2 Cell Division

17. 10-2 Cell Division Cell cycle • The G1, S and G2 phases are part of the interphase in the cell cycle. • The cell cycle is divided into four phases, which are: • G1 phase: the cell grows • S phase: DNA is replicated • G2 phase: The cell prepares to divide • M phase: mitosis and cytokinesis

18. 10-2 Cell Division Mitotic Phase • Unique to eukaryotes • Ends with 2 identical cells • Sub-stages of Mitosis: • Prophase • Metaphase • Anaphase • Telophase • Cytokenisis

19. 10-2 Cell Division Mitosis Back Prophase Metaphase Anaphase • Telophase Cell Cycle Cytokinesis

20. 10-2 Cell Division Prophase • Sister chromatids are attached at centromere • Centrioles separate and extend spindle fibers • Nucleolus disappears and nuclear envelope breaks down • Kinetochores form on each chromatid, spindle fibers attach

21. 10-2 Cell Division

22. 10-2 Cell Division

23. 10-2 Cell Division Prophase • During prophase, the chromosomes become visible. The centrioles take positions in opposite sides of the cell and form the spindle.

24. 10-2 Cell Division Metaphase • Centrosomes at poles • Chromosomes lined up at metaphase plate (cell’s equator) • Kinetochores of sister chromatids face opposite poles

25. 10-2 Cell Division

26. 10-2 Cell Division Metaphase • During metaphase, the chromosomes line up across the center of the cell. • Microtubules connect the centromere of each chromosome to the two poles of the spindle.

27. 10-2 Cell Division Anaphase • Spindle fibers pull sister chromatids apart forming daughter chromosomes • Chromosomes move centromere first towards opposite poles • Cell elongates

28. 10-2 Cell Division

29. 10-2 Cell Division Anaphase • During Anaphase, the centromeres that joined the sister chromatids split becoming individual chromosomes.

30. 10-2 Cell Division Telophase & Cytokenisis • Cell continues to elongate • Daughter nuclei appear at poles • Nuclear envelopes reform • Spindle fibers disappear • Cytoplasms separate, new cell membranes form

31. 10-2 Cell Division

32. 10-2 Cell Division Telophase • The chromosomes move to opposite sides of the cell and a nuclear envelope forms around each group of chromosomes.

33. 10-2 Cell Division Cytokenisis • Cell pinches into two cells • Called a cleavage furrow • Plants are a little different • Vesicles save materials from cell wall • Form a plate at center of dividing cell • Cell plate fuses to cell wall, 2 cells

34. 10-2 Cell Division Cytokinesis • The process in which the cytoplasm separates, forming completely the two new daughter cells. • It usually occurs about the same time as Telophase. • This occurs different in plants and in animals.

35. 10-2 Cell Division

36. 10-2 Cell Division

37. 10-2 Cell Division

38. 10-2 Cell Division

39. 10-2 Cell Division

40. 10-2 Cell Division

41. 10-2 Cell Division Animals • The cell membrane is drawn inwards until the cytoplasm is pinched into two nearly equal parts. • Each part contains its own nucleus and cytoplasmic organelles.

42. 10-2 Cell Division Plants • A structure known as 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.

43. Figure 10–5 Mitosis and Cytokinesis Section 10-2 Spindle forming Centrioles Centromere Chromatin Centriole Nuclear envelope Chromosomes (paired chromatids) Interphase Prophase Spindle Cytokinesis Centriole Metaphase Individual chromosomes Telophase Anaphase Nuclear envelope reforming

44. Figure 10–5 Mitosis and Cytokinesis Section 10-2 Spindle forming Centrioles Centromere Chromatin Centriole Nuclear envelope Chromosomes (paired chromatids) Interphase Prophase Spindle Cytokinesis Centriole Metaphase Individual chromosomes Telophase Anaphase Nuclear envelope reforming

45. Figure 10–5 Mitosis and Cytokinesis Section 10-2 Spindle forming Centrioles Centromere Chromatin Centriole Nuclear envelope Chromosomes (paired chromatids) Interphase Prophase Spindle Cytokinesis Centriole Metaphase Individual chromosomes Telophase Anaphase Nuclear envelope reforming

46. Figure 10–5 Mitosis and Cytokinesis Section 10-2 Spindle forming Centrioles Centromere Chromatin Centriole Nuclear envelope Chromosomes (paired chromatids) Interphase Prophase Spindle Cytokinesis Centriole Metaphase Individual chromosomes Telophase Anaphase Nuclear envelope reforming

47. Figure 10–5 Mitosis and Cytokinesis Section 10-2 Spindle forming Centrioles Centromere Chromatin Centriole Nuclear envelope Chromosomes (paired chromatids) Interphase Prophase Spindle Cytokinesis Centriole Metaphase Individual chromosomes Telophase Anaphase Nuclear envelope reforming

48. Figure 10–5 Mitosis and Cytokinesis Section 10-2 Spindle forming Centrioles Centromere Chromatin Centriole Nuclear envelope Chromosomes (paired chromatids) Interphase Prophase Spindle Cytokinesis Centriole Metaphase Individual chromosomes Telophase Anaphase Nuclear envelope reforming

49. 10-3 Regulating the Cell Cycle Regulating the Cell Cycle • Controls on cell division • Cell Cycle regulators • Uncontrolled cell growth

50. 10-3 Regulating the Cell Cycle Factors that Affect Cell Division • Most reasons are unknown • “Growth Factors” • Proteins need for division; if not present it stops (Cyclin-regulates timing of cell cycle) • Cell-cycle control system • A system of proteins in the cell that trigger & coordinates major events in the cell cycle • Make checkpoints