Cell Growth and Division

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