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Cellular Division

Cellular Division. When do Cells Divide?. Cells obtain nutrients and eliminate wastes through the cell membrane. There must be enough surface area for all of the exchanges to take place with the environment.

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Cellular Division

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  1. Cellular Division

  2. When do Cells Divide? • Cells obtain nutrients and eliminate wastes through the cell membrane. There must be enough surface area for all of the exchanges to take place with the environment. • It is more difficult for cells with a larger volume to transport, so cells remain relatively small to survive. • When a cell reaches its maximum size, the nucleus initiates cell division.

  3. Why do Cells Divide? • Cell division accounts for 3 essential life processes: • Growth - increase in size • Differentiation - cells develop specialized shapes and functions.

  4. Why do Cells Divide? • Cell division accounts for 3 essential life processes: • Repair - heal injuries by cell regeneration at the injury site

  5. Why do Cells Divide? • Cell division accounts for 3 essential life processes: • Reproduction - making new organisms • Asexual - offspring produced by one parent; the result of cell division • Sexual - offspring have a combination of genetic material from two parent organisms; requires meiosis, a specialized form of cell division

  6. How do Cells Divide? • Phase - a defined period within a cycle of change • Cell cycle - the sequence of phases in the life cycle of a cell

  7. The Cell Cycle

  8. Interphase • Interphase - growth and preparation • Occurs between divisions • 3 stages • G1 (gap 1) - growth and development • S (synthesis - chromosomes replicate; the cell commits to cell division • G2 (gap 2) - cell synthesizes other organelles and other materials needed for division

  9. Interphase • During interphase, the chromosomes are in chromatin form - a tangled bundle • During S phase, each chromosome is replicated, creating sister chromatids • As cell division begins (during prophase), the chromatin coils and condenses to chromosomes and the sister chromatids are clearly visible, joined at the centromere.

  10. Chromatin - uncoiled DNA • Chromosome - neatly coiled DNA

  11. Cell Division - Mitosis and Cytokinesis • There are 2 stages in cell division: • 1. Mitosis • The cell’s nucleus divides into 2 nuclei. • 2. Cytokinesis • The cell’s cytoplasm divides to make 2 daughter cells

  12. Mitosis • Mitosis is the splitting of the cell’s nucleus • It has 4 parts: • Prophase • Metaphase • Anaphase • Telophase

  13. Mitosis - Prophase • Chromosomes condense • In animal cells, a pair of centrioles migrates to each side of the cell • The mitotic spindle forms from the centrioles • The nuclear membrane and nucleolus dissappear

  14. Mitosis - Prophase

  15. Mitosis - Metaphase • Spindle arranges chromosomes along “metaphase plate”

  16. Mitosis - Anaphase • Centromeres divide and sister chromatids are pulled apart, so that each daughter cell has an identical set of chromosomes

  17. Mitosis - Telophase • Nuclear membrane reforms around each set of chromosomes • Two nucleoli form • Chromosomes uncoil into chromatin • Cleavage furrow starts to form (for cytokinesis)

  18. Cytokinesis • The cell’s cytoplasm divides to make 2 daughter cells • The cleavage furrow pinches cell in half

  19. Four Mitotic Stages • Prophase • Metaphase • Anaphase • Telophase

  20. Identical Daughter Cells Two identical daughter cells Parent Cell

  21. Mitosis in Animal Cells • Rat epithelial cells

  22. Mitosis in Plant Cells • Plant cells have a cell wall. • During mitosis, a cell plate forms a new cell membrane and cell wall between the two daughter cells.

  23. History • Mitosis was first observed microscopically in the 1870s by the German biologist Walter Flemming • He coined the term mitosis • from the Greek word mitos, • meaning thread

  24. The Cell Cycle Interphase may be up to 90% of the cell cycle. The time varies for different cell types.

  25. The Cell Cycle

  26. MeiosisFormation of Gametes(Eggs & Sperm)

  27. Facts About Meiosis • Produces sex cells called gametes (eggs & sperm) • Occurs in the testes in males (Spermatogenesis) • Occurs in the ovaries in females (Oogenesis)

  28. Facts About Meiosis • The gametes (eggs and sperm) are haploid - which means they have 1 set of chromosomes, not 2 like all of our diploid body cells. • Why we need meiosis --> this is critical for sexual reproduction.

  29. The Process of Meiosis • It starts with a diploid cell that has 46 chromosomes (2N). • The DNA is replicated, so there are 92 chromosomes. There are 4 copies of each, making a tetrad.

  30. The Process of Meiosis • The first division, very similar to mitosis, occurs, producing two cells with 46 chromosomes each. • A second division occurs, producing 4 haploid daughter cells that each have 23 chromosomes (N)

  31. Meiosis I MeiosisII Meiosis: Two Part Cell Division Diploid at start Diploid Haploid

  32. from mom from dad child too much! meiosis reduces genetic content Meiosis Forms Haploid Gametes • Meiosis must reduce the chromosome number by half • Fertilization then restores the 2n number The right number!

  33. Crossing-Over Pieces of chromosomes are exchanged, which produces genetic recombination in the offpsring

  34. Crossing-Over Crossing-over multiplies the number of different gamete types

  35. Fertilization 2N = 6 1N = 3

  36. Humans • Haploid number (1N) = 23 • Diploid number (2N) = 46 • Somatic cells are diploid. • Gametes are haploid.

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