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Mitosis. LH Biology – Spring 2012 Cell Division. Mitosis. Mitosis is the process where a ‘parent’ cell divides to produce two new, identical cells New cells are called ‘daughter’ cells THINK : Skin, hair, growth, and repair

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  1. Mitosis LH Biology – Spring 2012 Cell Division

  2. Mitosis • Mitosisis the process where a ‘parent’ cell divides to produce two new, identical cells • New cells are called ‘daughter’ cells • THINK: Skin, hair, growth, and repair • New cells are produced as you grow, heal, and during day-to-day living • ALL eukaryoticorganisms produce new cells through mitosis

  3. Cell Cycle • Consists of 2 broad stages • 1. Growing Stage called Interphase • 2. Cell Division called Mitotic Phase (M Phase) • The majority of the cell cycle is spent in Interphase (90%) • Consists of 3 parts: G1, S, G2

  4. Interphase – G1 • Occurs BEFOREMitosis begins • G1 – “first gap” • Cell begins to grow • Growth continues through S Phase 2n 2n G1 Phase

  5. Interphase – S Phase • S Phase – • DNA Replication occurs • Chromosomes are duplicated (DNA copied) • Chromosomes appear as threadlike coils • Made of Chromatin, a combination of DNA and protein molecules G1: 23 mom 23 dad S: STILL 23 mom & 23 dad but DNA has been doubled

  6. Interphase – S Phase • As the cell prepares to divide, its chromatin fibers condense, becoming the compact structure we call a chromosome. • Chromosomes are copied (# doubles) • Centrosome is copied too  now TWOcentrosomes! • Each chromosome is “made” of twosister chromatidsheld together by a centromere Uncoiled chromosomes (CHROMATIN) 2 chromosomes = 4 chromatids NUCLEUS

  7. Interphase – G2 • G2 Phase (“second gap”) • G2 – Continues growing and prepares for cell division Parent chromosomes After copying, the two identical chromosomes are now called sister chromatids

  8. Refresher……. The Cell Cycle G1 phase: Growth S phase: DNA replication G2 phase: Final preparation for cell division M phase: Mitosis and Cytokinesis

  9. Mitotic Phase • After Interphase, Mitotic Phase begins • Two parts of M Phase: • Mitosis • Cytokinesis

  10. M Phase • Mitosis– the nucleus and duplicated chromosomes divide and create two identical daughter cells • Cytokinesis– the process by which the cytoplasm is divided in two • Cytokinesis usually begins before Mitosis is completed centromere cytokinesis

  11. Prophase First phase of Mitosis: • Nuclear envelope breaks down 2. Chromatin becomes tightly coiled = chromosome  condense & organize 3. Spindle begins to form in the cytoplasm (produced by the centrioles) 4. Centrosomes begin to move apart. Note: there are 2 centrioles inside each centrosome! centrosomes

  12. Metaphase Second phase of Mitosis: • Nuclear membrane disappears • Chromosomes line up in the middle of the cell forming an equator 3. Chromosomes attach to the spindle at the centromeres (belts) Note: Remember, in human cells, we have 46 chromosomes (not 4 like above…)

  13. Anaphase Third phase of Mitosis: • Spindle pulls apart the chromosomes • Chromatids separate at the centromere and move towards each end • NOTE: Each chromatid is now considered a chromosome  b/c it is no longer connected via the centromere **cell now has double the chromosomes

  14. Anaphase by the #s • When the chromosomes split at the end of metaphase, the chromosome number is doubled. • For example, the number of chromosomes and chromatids during each phase in a human cell is:

  15. Telophase Fourth phase of Mitosis: • Chromosomes reach end of spindle • Spindle breaks down • Cleavage furrow begins to form • Nuclear membrane begins to reform

  16. Cytokinesis Final Phase of Cell Division/M Phase • Cleavage furrow pinches all the way through • Result is two new cells • 2 cells then enter Mitosis & begin again! • G1, S, G2 (Interphase) • PMAT & Cytokinesis • Each new cell at the end of mitosis is DIPLOID  has a full set of chromosomes

  17. To Help You Remember…. Interphase Prophase Metaphase Anaphase Telophase Cytokinesis IPMATC IPlayMonopolyATCamp

  18. Cell division Plants vs. Animals • B/c of the cell wall found in plants, cytokinesis does not involve a cleavage furrow • During telophase, vesicles line up in the middle of the cell • Contain cell wall material • Vesicles fuse  forms the cell plate • a double membrane across the midline of a dividing plant cell, between which the new cell wall forms during cytokinesis

  19. Cell division Plants vs. Animals • Cell plate grows outward • More vesicles continue to fuse with it • Finally, the cell plate membrane fuses with the PM  two new daughter cells result • Each have their own cell wall and PM

  20. Prokaryotes - Binary Fission • Unlike eukaryotic organisms, prokaryotes produce new cells through a different process called binary fission. • Ex: bacteria • Process of Binary Fission: • 1. Duplication of chromosomes • 2. Elongation of the cell • 3. Division = two daughter cells

  21. Prokaryotes - Binary Fission • Duplication of chromosomes • DNA replication begins at the origin of replication • One copy of the DNA moves toward the opposite end of the cell

  22. Prokaryotes - Binary Fission • As DNA is duplicated, the cell is elongating • Once chromosomal duplication is complete, the bacteria is approx. twice its original size • PM has grown inward  divides parent cell into TWO daughter cells • Division is dependent on: • Nutrients available • Oxygen • On average, binary fission takes between 15-20 minutes

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