CHAPTER 10: CELL DIVISION

1. CHAPTER 10: CELL DIVISION Lab Biology CP

2. Chapter 10: Cell Division • 10.1 Cell Growth, Division, and Reproduction • 10.2 The Process of Cell Division • 10.3 Regulating the Cell Cycle • 10.4 Cell Diffentiation

3. 10.1 Cell Growth, Division, and Reproduction

4. Information “Overload” • Living cells store critical information in DNA. • As a cell grows, that information is used to build the molecules needed for cell growth. • As size increases, the demands on that information grow as well. If a cell were to grow without limit, an “information crisis” would occur.

5. Information “Overload” • Compare a cell to a growing town. The town library has a limited number of books. As the town grows, these limited number of books are in greater demand, which limits access. • A growing cell makes greater demands on its genetic “library.” If the cell gets too big, the DNA would not be able to serve the needs of the growing cell.

6. Exchanging Materials • Food, oxygen, and water enter a cell through the cell membrane. Waste products leave in the same way. • The rate at which this exchange takes place depends on the surface area of a cell. • The rate at which food and oxygen are used up and waste products are produced depends on the cell’s volume. • The ratio of surface area to volume is key to understanding why cells must divide as they grow.

7. Ratio of Surface Area to Volume Imagine a cell shaped like a cube. As the length of the sides of a cube increases, its volume increases faster than its surface area, decreasing the ratio of surface area to volume. If a cell gets too large, the surface area of the cell is not large enough to get enough oxygen and nutrients in and waste out.

8. Traffic Problems • To use the town analogy again, as the town grows, more and more traffic clogs the main street. It becomes difficult to get information across town and goods in and out. • Similarly, a cell that continues to grow would experience “traffic” problems. If the cell got too large, it would be more difficult to get oxygen and nutrients in and waste out.

9. Division of the Cell • Before a cell grows too large, it divides into two new “daughter” cells in a process called cell division. • Before cell division, the cell copies all of its DNA. • It then divides into two “daughter” cells. Each daughter cell receives a complete set of DNA. • Cell division reduces cell volume. It also results in an increased ratio of surface area to volume, for each daughter cell.

10. Asexual Reproduction • In multicellular organisms, cell division leads to growth. It also enables an organism to repair and maintain its body. • In single-celled organisms, cell division is a form of reproduction.

11. Asexual Reproduction (Mitosis) • Asexual reproduction is reproduction that involves a single parent producing an offspring. The offspring produced are, in most cases, genetically identical to the single cell that produced them. • Asexual reproduction is a simple, efficient, and effective way for an organism to produce a large number of offspring. • Both prokaryotic and eukaryotic single-celled organisms and many multicellular organisms can reproduce asexually.

12. Examples of Asexual Reproduction • Bacteria reproduce by binary fission.  •  Kalanchoe plants form plantlets. • Hydras reproduce by budding. 

13. Sexual Reproduction (Meiosis) • In sexual reproduction, offspring are produced by the fusion of two sex cells – one from each of two parents. These fuse into a single cell before the offspring can grow. • The offspring produced inherit some genetic information from both parents, but are genetically different. • ***Most animals and plants, and many single-celled organisms, reproduce sexually.

14. Comparing Sexual and Asexual Reproduction

15. 10.2 The Process of Cell Division

16. Chromosomes • The genetic information that is passed on from one generation of cells to the next is carried by chromosomes. • Every cell must copy its genetic information before cell division begins. • Each daughter cell gets its own copy of that genetic information. • Cells of every organism have a specific number of chromosomes. Humans have 46 chromosomes.

17. Prokaryotic Chromosomes • Prokaryotic cells lack nuclei. Instead, their DNA molecules are found in the cytoplasm. • Most prokaryotes contain a single, circular DNA molecule, or chromosome, that contains most of the cell’s genetic information.

18. Eukaryotic Chromosomes • In eukaryotic cells, chromosomes are located in the nucleus, and are made up of chromatin.

19. Chromatin is composed of DNA and histone proteins.

20. DNA coils around histone proteins to form nucleosomes.

21. The nucleosomes interact with one another to form coils and supercoils that make up chromosomes. http://www.youtube.com/watch?v=qIe4-fVjmPE

22. The Prokaryotic Cell Cycle • The prokaryotic cell cycle is a regular pattern of growth, DNA replication, and cell division. • Most prokaryotic cells begin to replicate, or copy, their DNA once they have grown to a certain size. • When DNA replication is complete, the cells divide through a process known as binary fission. • The end result is 2 identical daughter cells.

23. The Prokaryotic Cell Cycle • Binary fission is a form of asexual reproduction during which two genetically identical cells are produced. • For example, bacteria reproduce by binary fission. • http://www.youtube.com/watch?v=J6akNYlkehY

24. The Eukaryotic Cell Cycle • The eukaryotic cell cycle consists of four phases: G1, S, G2, and M. • Interphase is the time between cell divisions. • It is a period of growth that consists of the G1, S, and G2 phases. • The M phase is the period of cell division. http://www.sumanasinc.com/webcontent/animations/content/mitosis.html

25. G1 Phase: Cell Growth • In the G1 phase, cells increase in size and synthesize new proteins and organelles.

26. S Phase: DNA Replication • In the S (or synthesis) phase, new DNA is synthesized when the chromosomes are replicated.

27. G2 Phase: Preparing for Cell Division • In the G2 phase, many of the organelles and molecules required for cell division are produced.

28. M Phase: Cell Division • In eukaryotes, cell division occurs in two stages: mitosis and cytokinesis. • Mitosis is the division of the cell nucleus. • Cytokinesis is the division of the cytoplasm.

29. Important Cell Structures Involved in Mitosis • Chromatid– each strand of a duplicated chromosome • Centromere– the area where each pair of chromatids is joined • Centrioles– tiny structures located in the cytoplasm of animal cells that help organize the spindle • Spindle– a fanlike microtubule structure that helps separate the chromatids

30. Prophase • 1st phase of mitosis • Duplicated chromosomes condense and become visible • Centrioles move to opposite sides of nucleus and help organize the spindle • Spindle forms and DNA strands attach at a point called the centromere • The nucleolus disappears and nuclear envelope breaks down

31. Metaphase • 2nd phase of mitosis • Duplicated chromosomes use centromeres to line up across the center of the cell • The spindle fibers from each pole connect the centromere

32. Anaphase • 3rd phase of mitosis • Centromeres pulled apart • Chromatids separate to become individual chromosomes • Chromosomes separate into two groups near the poles of the spindle

33. Telophase • 4th and final phase of mitosis • The chromosomes spread out into a tangle of chromatin • The nuclear envelope reforms around each group of chromosomes • The spindle breaks apart • Nucleolus becomes visible in each daughter nucleus

34. Cytokinesis • Cytokinesis is the division of the cytoplasm. • The process of cytokinesis is different in animal and plant cells.

35. Cytokinesis in Animal Cells • The cell membrane is drawn in until the cytoplasm is pinched into two equal parts. • Each part contains its own nucleus and organelles.

36. Cytokinesis in Plant Cells • In plants, the cell membrane is not flexible enough to draw inward because of the rigid cell wall. • Instead, a cell plate forms between the divided nuclei that develops into cell membranes. • A cell wall then forms in between the two new membranes. http://www.youtube.com/watch?v=3kpR5RSJ7SA (mitosis)

37. The Stages of the Cell Cycle Interphase Prophase Metaphase Cytokinesis Telophase Anaphase

38. 2 sex cells (egg and sperm) come together Fertilization: joining of an egg and sperm Form a zygote Sexual Reproduction

39. Diploid and Haploid Cells • Diploid Cells: • When cells have pairs of similar chromosomes • 46 chromosomes or 23 pairs • Example: body cells • Haploid Cells: • No pairs (only ½ the number of chromosomes) • 23 chromosomes • Example: sex cells

40. Meiosis: a process that produces haploid sex cells Meiosis I Prophase I Metaphase I Anaphase I Telophase I Meisois II Prophase II Metaphase II Anaphase II Telophase II Sexual Reproduction: Meiosis

41. Meiosis I

42. Meiosis II

43. Mitosis vs. Meiosis • Mitosis: • 2 new cells • Asexual reproduction • Daughter cells IDENTICAL to parent cells • Meiosis: • 4 new cells • Sexual reproduction • Daughter cells NOT identical to parent cells

44. 10.3 Regulating the Cell Cycle

45. The timing on cell growth and cell division can be turned on and off. • For example, when an injury such as a broken bone occurs, cells are stimulated to divide rapidly and start the healing process. The rate of cell division decreases when the healing process nears completion.

46. The Discovery of Cyclins • Cyclinsare a family of proteins that regulate the timing of the cell cycle in eukaryotic cells. • This graph shows how cyclin levels change throughout the cell cycle in fertilized clam eggs.

47. Apoptosis • Apoptosis is a programmed cell death. • Apoptosis plays a role in development by shaping the structure of tissues and organs in plants and animals.

48. Cancer is a disorder in which body cells lose the ability to control cell growth. • Cancer cells divide uncontrollably to form a mass of cells called a tumor. http://www.youtube.com/watch?v=qjjHKDn12qI&feature=related http://www.youtube.com/watch?v=LEpTTolebqo&feature=related

49. A benign tumor is noncancerous. It does not spread to surrounding healthy tissue. A malignant tumor is cancerous. It invades and destroys surrounding healthy tissue and can spread to other organs of the body.

50. What Causes Cancer? • Cancers are caused by defects in genes that regulate cell growth and division. • Some sources of gene defects are smoking or chewing tobacco, radiation exposure, defective genes, and viral infections. • A damaged or defective p53 gene is common in cancer cells. It causes cells to lose the information needed to respond to growth signals.