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THE CELL CYCLE

THE CELL CYCLE. The Cell Cycle Events that occur in the life of a cell. Includes 3 major stages: Interphase Mitosis Cytokinesis. 1. Interphase (Cell is not dividing) G 1 Phase – carries out basic functions & performs specialized activities. duration is extremely variable

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THE CELL CYCLE

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  1. THE CELL CYCLE

  2. The Cell Cycle Events that occur in the life of a cell. Includes 3 major stages: • Interphase • Mitosis • Cytokinesis

  3. 1. Interphase (Cell is not dividing) • G1 Phase – carries out basic functions & performs specialized activities. • duration is extremely variable • contains restriction checkpoint ~ cell “decides” to: • divide • enter a quiescent phase (G0) • die

  4. 1. Interphase (Cell is not dividing) • G0 Phase – cell maintains specialized characteristics, but does not divide Ex. neurons & muscle cells

  5. 1. Interphase (Cell is not dividing) • S Phase – cell replicates chromosomes & synthesizes proteins • animal cells replicate centrioles as well

  6. 1. Interphase (Cell is not dividing) • G2 Phase - cell synthesizes additional proteins (ex. tubulin) & assembles/stores membrane material

  7. Mitosis (M phase) – Equal distribution of replicated genetic material. • Five steps: • Prophase • Prometaphase • Metaphase • Anaphase • Telophase

  8. Mitosis – Prophase • replicated chromosomes condense • centrosomes separate & migrate toward opposite sides of cell • mitotic spindle forms (microtubules grow out from centrosomes) • nucleolus disappears

  9. Mitosis – Prometaphase • nuclear membrane breaks down • spindle fibers attach to centromeres of chromosomes

  10. Mitosis – Metaphase • chromosomes are lined up single-file along equator of mitotic spindle

  11. Mitosis – Anaphase • Centromeres part, sister chromatids (now called chromosomes) separate • chromosomes move toward opposite poles

  12. Mitosis – Telophase • mitotic spindle breaks down • chromosomes decondense • nuclear membranes reform around two nuclei • nucleoli reappear

  13. Cytokinesis • Distribution of cytoplasm to daughter cells • begins during anaphase or telophase • differs in animal & plant cells

  14. Cytokinesis in animal cells • Cleavagefurrow (slight indentation) forms around equator of cell • Actin & myosin microfilaments act like a drawstring to pinch the cell in two • Usually an equal division

  15. Cytokinesis in plant cells • phragmoplast (microtubule structure) forms in cytoplasm & traps vesicles containing cell wall material • vesicles fuse, forming a cell plate across midline of cell • cell plate gives rise to two primary cell walls

  16. Review of the M-phase

  17. Review of the M-phase

  18. Review of the M-phase

  19. Review of the M-phase

  20. Review of the M-phase

  21. Review of the M-phase

  22. Review of the M-phase

  23. Review of the M-phase

  24. Review of the M-phase

  25. Review of the M-phase

  26. Does cytokinesis always accompany karyokinesis? Karyokinesis in the absence of cytokinesis results in a syncytium(mass of multinucleated cells).

  27. Control of the Cell Cycle Checkpoints - groups of interacting proteins that ensure cell cycle events occur in the correct sequence.

  28. Shortening of telomeres - loss of telomere DNA signals cell to stop dividing. Some cells produce telomerase(enzyme that continually adds telomere DNA).

  29. Contact Inhibition - healthy cells stop dividing when they come in contact with other cells.

  30. Hormones - stimulate cell division. Ex. Estrogen stimulates uterine cell division Growth factors - proteins that stimulate local cell division. Ex. Epidermal growth factor (EGF) stimulates epithelial cell division filling in new skin underneath a scab Interaction of kinases & cyclins - activate genes that stimulate cell division.

  31. B. Apoptosis Programmed cell death; part of normal development.

  32. Steps of Apoptosis:

  33. C. Cancer (loss of cell cycle control) Condition resulting from excess cell division or deficient apoptosis. Characteristics of Cancer Cells: • can divide uncontrollably & eternally • are heritable & transplantable • lack contact inhibition • readily metastasize • exhibit angiogenesis • exhibit genetic mutability

  34. Causes of Cancer: • Over-expression of oncogenes Oncogenes are genes that trigger limited cell division. • Inactivation of tumor suppressor genes Tumor suppressor genes prevent a cell from dividing or promote apoptosis.

  35. Normal functioning of oncogenes & tumor suppressor genes may be affected by environmental factors: • carcinogens • radiation • viruses • diet • exercise habits

  36. Meiosis - formation of gametes • Somatic cells – body cells • In contrast to mitosis (occurs in somatic cells), gametes (eggs or sperm) are produced only in gonads (ovaries or testes). • In the gonads, cells undergo a variation of cell division (meiosis) which yields four daughter cells, each with half the chromosomes of the parent. • In humans, meiosis reduces the number of chromosomes from 46 to 23 • Chromosomes #1 through 22 – autosomal • Chromosome #23 – sex

  37. Meiosis - formation of gametes • Fertilization fuses two gametes together and doubles the number of chromosomes to 46 again. • Organisms inherit single copy of each gene from each parent • These copies are segregated from each other during formation of the gametes • Homologous – corresponding male and female chromosomes

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