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Review

Review. What is the purpose of mitosis? What is the cell cycle? What are the phases of mitosis? Describe at least one event from each phase. Chapter 12: The Cell Cycle. Rudolf Virchow-1855 “Omnis cellula e cellula” Every cell from a cell.

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Review

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  1. Review • What is the purpose of mitosis? • What is the cell cycle? • What are the phases of mitosis? • Describe at least one event from each phase.

  2. Chapter 12: The Cell Cycle • Rudolf Virchow-1855 “Omnis cellula e cellula” • Every cell from a cell. • Cells reproduce to form genetically equivalent daughter cells.

  3. Roles of Cell Division • Reproduction • Growth • Repair • In all cases, cell division must distribute identical genetic material to two daughter cells.

  4. Genome • The cell's hereditary endowment of DNA. • Usually packaged into chromosomes for manageability. • Chromosomes • Made of a DNA and protein complex called Chromatin. • During cell division, the chromatin becomes highly condensed into the chromosomes.

  5. Chromosomes - Structure • At cell division, each chromosome has been duplicated. • The duplicated chromosome consists of two sister chromatids.

  6. Cell Cycle - parts 1. Interphase - (90% of cycle) - when the cell grows and duplicates the chromosomes. • Mitotic Phase (M) - when the chromosomes are split into separate cells. • Mitosis – equal division of replicated chromosomes, by separation of the sister chromatids into separate cells. • Cytokinesis - division of the cell’s cytoplasm.

  7. Cell grows and carries out regular biochemical functions. When the DNA is replicated or synthesized. Cell completes preparations for division. Centrosomes and organelles are replicated.

  8. Interphase Centrosome, made of two centrioles is replicated.

  9. Mitosis Steps • Prophase • Prometaphase • Metaphase • Anaphase • Telophase

  10. Prophase

  11. Prophase • Nucleoli disappear. • Chromatin condenses into the chromosomes. • Centrosomes separate to opposite ends of the cell. • Mitotic spindle begins to form.

  12. Prophase

  13. Prometaphase

  14. Prometaphase • Nuclear envelope dissolves. • Spindle fibers attach to the kinetochore (a structure of proteins and specific sections of chromosomal DNA) of the centromeres.

  15. Prometaphase

  16. Metaphase - movie

  17. Metaphase • Centrosomes now at opposite ends of the cell. • Chromosomes line up on the metaphase plate. • Spindle apparatus fully developed.

  18. Metaphase

  19. Anaphase

  20. Anaphase • Centromeres break and the duplicate chromosomes are pulled away from each other toward opposite ends of the cell. • Kinetochore appear to “ratchet” the chromosome down the spindle fiber microtubule with a motor protein. • Microtubules dissolve behind the kinetochore (shown with laser microbeam wxperiment) • Cell elongates; poles move slightly further apart.

  21. Microtubules shorten only on the kinetochore side.

  22. Anaphase

  23. Telophase

  24. Telophase • Chromosomes uncoil back to chromatin. • Nuclear envelope reforms. • Nucleoli reappear. • Spindle fibers disappear. • Cytokinesis usually starts.

  25. Telophase

  26. Cyotkinesis

  27. Cytokinesis

  28. Cytokinesis • Animal • Cleavage furrow forms. • Microfilaments contracts and divides the cytoplasm into two parts. • Plants • Cell plate develops from Golgi vesicles. • New cell wall developed around the cell plate.

  29. Cell Plate

  30. Cell Division

  31. Animal Cell - Mitosis

  32. Plant Cell - Mitosis

  33. Evolution of Mitosis

  34. Regulation of Cell Division • Must be controlled. • Rate of cell division depends on the cell type. • Ex - skin: frequently • liver - as needed • brain - rarely or never

  35. Checkpoints • A critical control point in the cell cycle. • Several are known. • Cells must receive a “go-ahead” signal before proceeding to the next phase. • G1 Checkpoint • Also called the “restriction point” in mammalian cells. • Places cells in a non-dividing phase called the Go phase.

  36. Go Phase • Non-dividing state. • Most cells are in this state. • Some cells can be reactivated back into M phase from the Go phase.

  37. Protein Kinase Checkpoint - G2 • Uses protein kinases to signal “go-ahead” for the G2 phase. • Activated by a protein complex whose concentration changes over the cell cycle. • M-phase Promoting Factor (MPF). • Protein complex required for a cell to progress from G2 to Mitosis. • Role of MPF - to trigger a chain of protein kinase activations.

  38. Active M-phase Promoting Factor (MPF) has: • Cdk (Cyclin dependent kinase) • is a Protein Kinases (activates and deactivates other proteins by phosphoryalating them. • Amount remains constant during cycle. • Inactive unless bound with cyclin. • When enough cyclin is present, active MPF is formed. • Cyclin • Protein whose concentration builds up over G1, S and G2, then falls abruptly during Mitosis.. • The activity of Cdk rises and falls with changes in the concentration of its cyclin partner. http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120082/bio34a.swf::Control%20of%20the%20Cell%20Cycle

  39. Active M-phase Promoting Factor (MPF) • Triggers Mitosis. • Activates a cyclin-degrading enzyme, which lowers the amount of cyclin in the cell. • Result - no active MPF to trigger another mitosis until the cycle is repeated. http://www.cellsalive.com/cell_cycle.htm http://bcs.whfreeman.com/lodish5e/content/cat_010/21010-01.htm?v=chapter&i=21010.01&s=21000&n=00010&o=00PRS

  40. Growth Factors • External signals that affect mitosis. • Examples: 1. Platelet-Derived Growth Factor (PDGF) • Stimulates cell division to heal injuries. 2. Density-dependent inhibition • The number of cells in an area force competition for nutrients, space, and growth factors . • When density is high - no cell division. • When density is low - cells divide. 3. Anchorage dependence

  41. PDGF

  42. Density-Dependent Inhibition

  43. Growth Factors (Continued) • External signals that affect mitosis. • Examples: • 3. Anchorage dependence • Inhibition of cell division unless the cell is attached to a substratum. • Prevents cells from dividing and floating off in the body.

  44. Cancer Cells • Do not stop dividing. The control mechanisms for cell division have failed.

  45. Comment • Regulation of cell division is a balance between: Mitosis - making new cells. Apoptosis - cell suicide. • Cancer can result if either process doesn’t work.

  46. Summary • Know the phases and steps of the cell cycle. • Be able to discuss the “regulation” of the cell cycle. mitosis tutorial http://www.sci.sdsu.edu/multimedia/mitosis/ onion cell mitosis activity http://www.biology.arizona.edu/Cell_BIO/activities/cell_cycle/cell_cycle.html Cell cycle animation http://www.cellsalive.com/cell_cycle.htm mitosis tutorial (U of Arizona) http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/main.html animal cell mitosis http://www.cellsalive.com/mitosis.htm

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