Mitosis

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Mitosis

  1. 1. Cellular Reproduction and the Cell Cycle
  2. 3. What do all cells require to survive? <ul><li>A complete set of genetic instructions </li></ul>– produce required molecules – direct life processes <ul><li>Genetic instructions are coded in </li></ul><ul><li>the DNA of cells </li></ul>
  3. 4. Why do cells divide? <ul><li>Growth </li></ul><ul><li>Repair </li></ul><ul><li>Development </li></ul>
  4. 5. Cell Cycle <ul><li>Activities of a cell from one cell </li></ul><ul><li>division to the next </li></ul>– Cell grows, adding more cytoplasmic constituents – DNA is replicated – cell divides into two identical daughter cells
  5. 6. Essential Feature of Cell Division <ul><li>Must ensure a complete copy of the genetic information is transferred to both daughter cells. </li></ul>
  6. 7. Two Fundamental Types of Cells (organisms): <ul><li>Prokaryotic </li></ul><ul><li>Eukaryotic </li></ul>
  7. 8. Prokaryotic Cell <ul><li>no nucleus – genetic material </li></ul><ul><li>(DNA) in cytoplasm </li></ul><ul><li>no membrane-bound organelles </li></ul><ul><li>example: bacteria </li></ul><ul><li>cell division is called binary fission </li></ul>
  8. 9. Eukaryotic Cell <ul><li>membrane-bound organelles, including </li></ul><ul><li>a nucleus </li></ul><ul><li>genetic material (DNA) contained within </li></ul><ul><li>the nucleus </li></ul><ul><li>examples: fungi, protists, plants, </li></ul><ul><li>animals </li></ul><ul><li>cell division of somatic cells called </li></ul><ul><li>mitotic cell division </li></ul>
  9. 10. During non-division phase of cell cycle <ul><li>DNA molecules in extended, </li></ul><ul><li>uncondensed form = chromatin </li></ul>– cell can only use DNA to produce molecules when in extended state
  10. 11. – easier to sort and organize DNA into daughter cells During division phase of cell cycle <ul><li>DNA molecules condense to form </li></ul><ul><li>chromosomes prior to division </li></ul>– each chromosome is a single molecule of DNA
  11. 13. Prokaryotic Cell Cycle <ul><li>Prokaryotic chromosome a circular loop </li></ul><ul><li>chromosome attaches to one point </li></ul><ul><li>on plasma membrane </li></ul><ul><li>chromosome is replicated </li></ul><ul><li>– replicated chromosome attached </li></ul><ul><li>to plasma membrane at a different </li></ul><ul><li>nearby point </li></ul>
  12. 14. <ul><li>cell elongates – new plasma </li></ul><ul><li>membrane is added between </li></ul><ul><li>between chromosomes, pushing </li></ul><ul><li>them towards opposite ends of cell </li></ul><ul><li>plasma membrane grows inward </li></ul><ul><li>at middle of cell </li></ul><ul><li>parent cell is divided into two </li></ul><ul><li>identical daughter cells </li></ul>
  13. 15. Cell wall Plasma membrane Chromosome
  14. 18. <ul><li>Division of somatic cells </li></ul><ul><ul><li>(non reproductive cells) in </li></ul></ul><ul><ul><li>eukaryotic organisms </li></ul></ul>What is Mitotic Cell Division? <ul><li>A single cell divides into two </li></ul><ul><li>identical daughter cells </li></ul><ul><li>(cellular reproduction) </li></ul>=> Maintains chromosome ploidy of cell
  15. 19. Ploidy – refers to the number of pairs of chromosomes in cells <ul><li>haploid – one copy of each </li></ul><ul><li>chromosome </li></ul><ul><li>– designated as “ n ” </li></ul><ul><li>diploid – two copies (= pair) of each </li></ul><ul><li>chromosome </li></ul><ul><li>– designated as “ 2n ” </li></ul>
  16. 20. Each species has a characteristic number of chromosomes: Prokaryotes – one chromosome Crayfish – 200 chromosomes Human – 46 chromosomes => 23 pairs of chromosomes
  17. 21. Diploid organisms receive one chromosome from female parent (= maternal ) and one chromosome from male parent (= paternal ) A “matched” pair of maternal and paternal chromosomes are called homologues
  18. 22. Structure of a eukaryotic chromosome <ul><li>unreplicated chromosome </li></ul>Chromatid Chromatid centromere
  19. 23. <ul><li>Prior to cell division: </li></ul><ul><li>chromosomes (DNA) are replicated </li></ul><ul><li>(duplicated) </li></ul>duplicated chromosome <ul><li>duplicated chromosome </li></ul><ul><li>– attached at their centromeres </li></ul><ul><li>– as long as attached, known as sister chromatids </li></ul>
  20. 24. daughter chromosomes sister chromatids
  21. 25. Eukaryotic Cell Cycle <ul><li>2 major phases: </li></ul><ul><li>Interphase (3 stages) </li></ul><ul><li>– DNA uncondensed (= chromatin) </li></ul><ul><li>Mitotic cell division (4 stages) </li></ul><ul><li>– DNA condensed (= chromosomes) </li></ul>
  22. 26. Interphase <ul><li>non-dividing state </li></ul><ul><li>3 stages: </li></ul>G 1 – cell grows in size – organelles replicated - majority of cell life span (90%) in this stage S – replication of DNA – synthesis of proteins associated with DNA
  23. 27. G 2 – synthesis of proteins associated with mitosis
  24. 28. Simplified cell cycle G 1 G 2 S Mitotic Cell Division
  25. 29. Mitotic Cell Division <ul><li>2 major processes: </li></ul><ul><li>mitosis – nuclear division </li></ul><ul><li>=> preserves diploid number of </li></ul><ul><li>chromosomes </li></ul><ul><li>cytokinesis – cytoplasmic division </li></ul><ul><li>=> cell divides into two daughter cells </li></ul>
  26. 30. Mitosis 4 phases: 1 st – Prophase (3 major events) 2 nd – Metaphase 3 rd – Anaphase 4 th – Telophase and Cytokinesis
  27. 31. Prophase i) chromosomes condense <ul><li>3 major events </li></ul>ii) spindle fibers form iii) chromosomes are captured by spindle
  28. 32. Chromosomes Condense <ul><li>Recall that chromosomes were </li></ul><ul><li>duplicated during interphase </li></ul><ul><li>=> each chromosome consists of </li></ul><ul><li>2 sister chromatids attached to </li></ul><ul><li>each other at the centromere </li></ul>
  29. 33. Mitotic Spindle Forms <ul><li>spindle fibers are specialized </li></ul><ul><li>microtubules (thin tubes) </li></ul><ul><li>spindle fibers radiate out from </li></ul><ul><li>centrioles , forming the “ aster ” </li></ul><ul><li>centrioles occur in pairs, and are </li></ul><ul><li>duplicated during interphase </li></ul>
  30. 34. <ul><li>one pair of centrioles migrates to </li></ul><ul><li>one pole of cell, the other pair </li></ul><ul><li>migrates to opposite pole of cell </li></ul>
  31. 35. Spindle Captures Chromosomes <ul><li>When spindle fibers are fully formed </li></ul><ul><li>nuclear envelope disintegrates and </li></ul><ul><li>nucleolus disappears </li></ul><ul><li>Spindle fibers attach to chromosomes </li></ul><ul><li>at the kinetochore , a structure located </li></ul><ul><li>at the centromere </li></ul>
  32. 36. sister chromatid sister chromatid centromere spindle fiber kinetochores centriole aster fibers
  33. 37. <ul><li>other spindle fibers do NOT attach </li></ul><ul><li>to chromosomes, but retain free </li></ul><ul><li>ends that overlap at cell’s equator </li></ul><ul><li>=> “ free spindle fibers ” </li></ul><ul><li>function of spindle fibers is to </li></ul><ul><li>organise division of sister chromatids </li></ul><ul><li>into daughter cells </li></ul>
  34. 38. chromatin nucleolus nucleus centrioles condensing chromosomes
  35. 39. Metaphase <ul><li>chromosomes align along </li></ul><ul><li>equator of the cell, with one </li></ul><ul><li>kinetochore facing each pole </li></ul>centrioles spindle fibers chromosomes
  36. 40. Anaphase <ul><li>sister chromatids separate </li></ul><ul><li>spindle fibers attached to </li></ul><ul><li>kinetochores shorten and pull </li></ul><ul><li>chromatids poleward </li></ul><ul><li>free spindle fibers lengthen and push </li></ul><ul><li>poles of cell apart </li></ul>
  37. 41. free spindle fibers V-shaped chromatid
  38. 42. Telophase <ul><li>spindle fibers disintegrate </li></ul><ul><li>nuclear envelope s form around both </li></ul><ul><li>groups of chromosomes </li></ul><ul><li>chromosomes revert to their extended </li></ul><ul><li>state </li></ul><ul><li>nucleoli reappear </li></ul>
  39. 43. <ul><li>cytokinesis occurs, enclosing each </li></ul><ul><li>daughter nucleus into a separate cell </li></ul>chromosomes decondensing nuclear envelope reforming nucleolus reappears pinching of cell membrane at equator
  40. 44. cytokinesis
  41. 45. Cytokinesis <ul><li>Animal cells: </li></ul><ul><li>– microfilaments attached to plasma </li></ul><ul><li>membrane form a ring around </li></ul><ul><li>equator of cell </li></ul><ul><li>– ring contracts, like a drawstring, </li></ul><ul><li>dividing the cytoplasm </li></ul>
  42. 46. <ul><li>Plant cells: </li></ul><ul><li>– stiff cell wall makes pinching </li></ul><ul><li>impossible </li></ul><ul><li>– Golgi complex buds off vesicles </li></ul><ul><li>filled with carbohydrate </li></ul><ul><li>– vesicles line up at equator and </li></ul><ul><li>fuse, producing a structure </li></ul><ul><li>called the cell plate </li></ul><ul><li>– cell plate becomes new cell wall </li></ul><ul><li>between the two cells </li></ul>
  43. 47. Mitotic Cell Division Functions: <ul><li>Growth, maintenance, repair of body </li></ul><ul><li>tissues </li></ul><ul><li>Forms the basis of </li></ul><ul><li>Asexual Reproduction </li></ul>
  44. 48. Summary of Mitosis <ul><li>Prophase: </li></ul><ul><ul><ul><li>Chromosomes condense </li></ul></ul></ul><ul><ul><ul><li>Nuclear envelope disappears </li></ul></ul></ul><ul><ul><ul><li>Spindles move to opposite sides of the cell </li></ul></ul></ul><ul><ul><ul><li>Spindle fibers attaches to centromeres on the chromosomes </li></ul></ul></ul><ul><li>Metaphase </li></ul><ul><ul><ul><li>Chromosomes lined up on equator of the cell </li></ul></ul></ul><ul><ul><ul><li>Spindles at opposite ends of cell </li></ul></ul></ul><ul><li>Anaphase </li></ul><ul><ul><ul><li>Centromeres snap </li></ul></ul></ul><ul><ul><ul><li>1 copy of each chromosome is pulled to opposite poles by the spindle </li></ul></ul></ul><ul><li>Telophase </li></ul><ul><ul><ul><li>Chromosomes de-condense </li></ul></ul></ul><ul><ul><ul><li>Nuclear envelope reappears </li></ul></ul></ul><ul><ul><ul><li>Cytoplasm divided into 2 cells </li></ul></ul></ul>
  45. 50. Cancer <ul><li>Cancer is a disease of uncontrolled cell division. It starts with a single cell that loses its control mechanisms due to a genetic mutation. That cell starts dividing without limit, and eventually kills the host. </li></ul><ul><li>Normal cells are controlled by several factors. They stay in the G1 stage of the cell cycle until they are given a specific signal to enter the S phase, in which the DNA replicates and the cell prepares for division. Cancer cells enter the S phase without waiting for a signal. </li></ul><ul><li>Another control: normal cells are mortal. This means that they can divide about 50 times and then they lose the ability to die. This “clock” gets re-set during the formation of the gametes. Cancer cells escape this process of mortality: they are immortal and can divide endlessly. </li></ul><ul><li>A third control: cells that suffer significant chromosome damage destroy themselves due to the action of a gene called “p53”. Cancer cells either lose the p53 gene or ignore its message and fail to kill themselves. </li></ul>
  46. 51. Cancer Progression <ul><li>There are many different forms of cancer, affecting different cell types and working in different ways. All start out with mutations in specific genes called “oncogenes”. The normal, unmutated versions of the oncogenes provide the control mechanisms for the cell. The mutations are caused by radiation, certain chemicals (carcinogens), and various random events during DNA replication. </li></ul><ul><li>Once a single cell starts growing uncontrollably, it forms a tumor, a small mass of cells. No further progress can occur unless the cancerous mass gets its own blood supply. “Angiogenesis” is the process of developing a system of small arteries and veins to supply the tumor. Most tumors don’t reach this stage. </li></ul><ul><li>A tumor with a blood supply will grow into a large mass. Eventually some of the cancer cells will break loose and move through the blood supply to other parts of the body, where they start to multiply. This process is called metastasis. It occurs because the tumor cells lose the proteins on their surface that hold them to other cells. </li></ul>
  47. 52. G2 Phase Production of mitosis proteins The Cell Cycle
  48. 53. Mitosis animation http://www.sci.sdsu.edu/multimedia/mitosis/mitosis_qt1.html

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