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Ch. 8: The Cell Cycle
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Ch. 8: The Cell Cycle

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  1. Ch. 8: The Cell Cycle

  2. Why does a cell divide? • As a cell absorbs nutrients and gets larger, the volume of the cell increases faster than the surface area. -Therefore, the demands of the cell (the volume) exceed the ability of the cell to bring in nutrients and export wastes. Solution? Divide into two smaller cells

  3. When is cell division occurring? GROWTH -increase number of cells REPAIR -replace lost cells due to injury, disease CANCER – Abnormally high rates of cell division due to mutation Different kinds of cells divide at different rates: E. coli – 20 minutes (What domain?) Yeast cell – 2 hours (What domain? What kingdom?) Amoeba – a few days (What domain? What kingdom?) Human embryo cell – 15-20 minutes Human adult cell – 8 hours to 100 days

  4. Aging All cells die after a certain number of divisions (programmed cell death-”apoptosis”). At any given time some cells are dividing and some cells are dying. Childhood Cell division > cell death Adulthood Cell division = cell death Aging Cell division < cell death

  5. Control of the Cell CycleCell proliferation

  6. Interphase Interphase ~ 90% of the time. ØG1: Little new cell absorbs nutrients and grows larger. Does protein synthesis, its job. ØS phase: Synthesis of new DNA (DNA replication) for daughter cells in preparation for mitosis. ØG2: Cell continues to grow, do protein synthesis, do its job. Gets too large, needs to divide.

  7. Chromosomes exist in 2 different states, before and after they replicate their DNA. Before replication chromosomes = 1 chromatid. After replication chromosomes = 2 sister chromatids, held together at the centromere. Each chromatid is one piece of DNA with its supporting proteins.

  8. Structure of a eukaryotic chromosome • unreplicated chromosome arm arm centromere

  9. duplicated chromosome – attached at their centromeres – as long as attached, known as sisterchromatids duplicated chromosome Prior to cell division: • chromosomes (DNA) are replicated (duplicated)

  10. sister chromatids daughter chromosomes

  11. What is Mitotic Cell Division? • Division of somatic cells (body cells) (non reproductive cells) in eukaryotic organisms • A single cell divides into two identical daughter cells (cellular reproduction) => Maintains chromosome ploidy of cell

  12. MITOSIS Equal distribution of the 2 sets of DNA amongst the 2 daughter cells. 4 Stages: “PMAT” 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase How the Cell Cycle Works Mitosis Animation Cell Cycle

  13. As a cell enters mitosis from interphase it has 2 complete sets of chromosomes because of replication in the S phase. Each set must be re-arranged and distributed into the 2 new daughter nuclei. This is mitosis.

  14. Prophase… • Chromatin condenses (coils) into chromosomes. (Sister chromatids joined by centromere) • Nuclear membrane dissolves. • Nucleolus disappears. • Centrioles divide and move to opposite poles forming spindle b/w them.

  15. condensing chromosomes chromatin nucleus nucleolus centrioles

  16. Metaphase -Sister chromatids line up on metaphase plate. -Centromeres lock on to spindle fibers

  17. Anaphase • Centromeres divide. • Spindle fibers contract pulling sister chromatids apart to poles.

  18. Telophase:New nuclear membranes form around new nuclei Mitosis Movie

  19. CYTOKINESIS – Cytoplasm splits into 2 cells. Animal cells: Cleavage furrow forms from outside in. Plant cells: Division/cell plate forms from inside out.

  20. Cell now returns to interphase . The chromosomes uncoil back into chromatin. The whole cell cycle starts over again….. http://www.cellsalive.com/mitosis.htm

  21. At any point in time the cells in a tissue will be at different stages in the cell cycle.

  22. Mitosis Stages Put these in the correct order..

  23. The Guarantee of Mitosis… • The 2 daughter cells formed are identical to each other and identical to the mother cell. • Why is this so important?

  24. Mitosis

  25. Whitefish Blastula

  26. Mitosis in Plant Cells

  27. Onion Root Tip

  28. Ch. 8: The Cell Cycle

  29. Mitosis

  30. Whitefish Blastula

  31. Mitosis in Plant Cells

  32. Onion Root Tip

  33. Controls on the Cell Cycle: 1. Cell Type: Some cells stop dividing when mature (stay in G0) Ex: neurons & muscle cells • Growth factors – protein that stimulates cell division • Density-dependent inhibition (cell to cell contact) Cells stop growing when they touch other cells • Anchorage (cells may required contact with a surface for cell division)

  34. Cell Cycle Regulators: Intracellular factors: • Checkpoints & Cyclins: All chromosomes are replicated? All spindles are attached? Are there enough mitochondria, etc.. If cells “pass” these checkpoints, the next stage of cell cycle begins. Cyclins = that start/stop cell cycle progression based on checkpoints Extra-cellular factors: • Binding of growth factors • Cell to cell contact

  35. Cell Cycle Regulators: Cyclins operate at checkpoints

  36. Cell Cycle Controls: External to Cell

  37. Growing Out of Control: Cancer • Cancer is a disease of the cell cycle • Cells do not respond normally to controls of the cell cycle system • Tumor: abnormally growing mass of body cells • Benign: abnormal cells remain at original sight forming a lump; although can cause problems, normally can be fully removed by surgery • Malignant: “cancerous” spread, displacing normal tissue and disrupting organ function • Metastasis: spread of cancer cells via circulatory system transport (traveling cancer cells) http://www.cancer.gov/cancertopics/understandingcancer/cancer/page2

  38. Molecular Basis of Cancer: • Tumor Suppressor Genes: - genes that normally halt the cell cycle - problem if stuck “OFF” (cells keep dividing) • Oncogenes: - genes that tell cells to divide - problem if stuck “ON” (cells keep dividing)

  39. Cancer categorized based on site of origin: (Not on quiz) • Carcinoma: originate in internal or external coverings of the body (skin or lining of intestine) • Sarcoma: Arise in support tissue (bone or muscle) • Leukemia: Arise in blood or bone marrow (abnormal number of white blood cells) • Lymphoma: Arise in lymphatic cells of the immune system (lymph nodes or spleen)

  40. Treating Cancer • Surgical removal of tumor • Radiation: • Damages DNA in cancer cells more than normal cell • Cancer cells do not have the ability to repair • Cancer cells die without dividing/reproducing • Chemotherapy: (For widespread or metastatic tumors) • Chemicals that disrupt specific steps in the cell cycle • freezes the mitotic spindle • prevents formation of spindle • Damage DNA or RNA involved in making growth factors

  41. Controls on the Cell Cycle: • Some cells stop dividing when mature (stay in G0) ex) many neurons (nerve) & muscle cells • Others divide for growth & repair • Influences of cell division: • Growth factors – protein that stimulates cell division • Density-dependent inhibition (cell to cell contact)

  42. Cell Cycle Regulators: • Proteins calledcyclins start/stop the cell cycle. • The cycle is regulate by various factors: • Intracellular factors(Checkpoints) • All chromosomes are replicated • All spindles are attached • Extra-cellular factors: • Binding of growth factors • Cell to cell contact

  43. Growing Out of Control: Cancer • a disease of the cell cycle • Cells do not respond normally to controls of the cell cycle system • Tumor: abnormally growing mass of body cells • Benign: abnormal cells remain at original sight forming a lump; although can cause problems, normally can be fully removed by surgery • Malignant: spread, displacing normal tissue and disrupting organ function • Metastasis: spread of cancer cells via circulatory system transport See slide show http://www.cancer.gov/cancertopics/understandingcancer/cancer/page2

  44. Molecular Basis of Cancer: • Tumor Suppressor Genes: - genes that normally halt the cell cycle - problem if stuck “OFF” (cells keep dividing) • Oncogenes: - genes that tell cells to divide - problem if stuck “ON” (cells keep dividing)

  45. Treating Cancer • Surgical removal of tumor • Radiation: • Damages DNA in cancer cells more than normal cell • Cancer cells do not have the ability to repair • Cancer cells die without dividing/reproducing • Chemotherapy: (For widespread or metastatic tumors) • Chemicals that disrupt specific steps in the cell cycle • freezes the mitotic spindle • prevents formation of spindle • Damage DNA or RNA involved in making growth factors