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Cell Growth and Division

Cell Growth and Division. Process, Regulation, and Cancer. Why are there limits to cell Size?. Demands placed on the DNA Difficulty moving enough wastes and nutrients across the cell membrane. Surface Area to Volume Ratio in a growing cell. The Cell Cycle.

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Cell Growth and Division

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  1. Cell Growth and Division Process, Regulation, and Cancer

  2. Why are there limits to cell Size? • Demands placed on the DNA • Difficulty moving enough wastes and nutrients across the cell membrane

  3. Surface Area to Volume Ratio in a growing cell.

  4. The Cell Cycle • M phase- Mitosis division of nucleus • G1 phase- Cells grow • S phase- synthesis of DNA molecules (replication of chromosomes) • G2- organelles and molecules for division made

  5. Life Span of some Cells • Intestinal cells divide every 3 days • Red blood cells live 120 days (approx 10 million made every second) • Nerve cells usually do not divide • Embryo shows almost constant cell division: 1 cell to several trillion cells in 9 months.

  6. Mitosis • Chromosomes replicated prior to division (S phase) • Each chromosome now made of two sister chromatids • Held together by a centromere

  7. Interphase • Stage not part of mitosis • Includes G1, S, and G2 stages • Lots of activity in the cell • Cell is NOT dividing

  8. Prophase • Centrioles migrate to poles • Mitotic spindle forms • Chromatin condenses to form chromosomes • Nuclear membrane disappears.

  9. Metaphase • Chromosomes line up at the middle of the cell

  10. Anaphase • Chromosomes separate • Spindle fibers shorten

  11. Telophase • Chromosomes arrive at poles • Chromosomes decondense become mass of chromatin • Spindle disappears • Nuclear membrane reforms • Nucleoli reappear

  12. Cytokinesis • Daughter cells are pinched apart • Plants: New cell membrane appears as vesicles, new wall forms. • Animals: cells pinched apart by contraction of microfilaments

  13. Mitosis Animation • Animation • Mitosis Video

  14. Cell Cycle needs to be regulated. • Cells should only divide when needed • Why? • How?

  15. Cycle Regulators • Cyclins: proteins that appear to regulate the timing of the cell cycle in eukaryotic cells. • Internal regulators: ex: p53 a protein that makes sure cell does not divide until all chromosomes have been replicated • External regulators: proteins from other cells that regulate the growth of neighbor cells.

  16. Contact Inhibition

  17. Cancer: Gene Regulation gone Wrong • Proto-oncogenes: genes whose products stimulate normal progress through cell cycle • Tumor suppressor genes: genes whose products prevent or inhibit progress through the cell cycle. Examples include p53 and pRB • Oncogenes: genes whose products promote tumor formation. Usually mutated proto-oncogenes.

  18. Formation of Oncogenes

  19. Two Pathways: Same Result

  20. Two major mutations in cancer • 40% of all human cancers have mutation in gene for pRB. Acts as master brake that keeps cell arrested in G1 phase. • Approx. 50% of human cancers contain mutations in gene for p53. p53 is an inhibitory control of several steps in cell cycle. • There are many others.

  21. What causes the mutations? • Name as many compounds as you can.

  22. Development of a Cancer

  23. Spread of Cancer

  24. How do we treat it? • Early detection: self exams, pap smear, rectal exams, tests for proteins or compounds in blood or urine (under development) • Genetic susceptibility: development of tests to reveal inherited mutations in proto-oncogenes and tumor suppressor genes.

  25. Traditional treatments • Surgery • Radiation therapy: damages DNA and induces expression of tumor suppressor genes. • Chemotherapy: relies on drugs that are detrimental to actively dividing cells. • Intestinal lining- nausea etc. • Bone marrow- anemia, loss of immunity • Hair follicles- loss of hair

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