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  1. 1. Why Do Cells Need To Divide? It depends on the organism Unicellular organisms like bacteria (prokaryotes) divide to reproduce Multicellular organisms (most eukaryotes) use it to grow larger and repair damaged cells.
  2. 2. 3 Types of Cell Division 1. Binary fission-cell division in prokaryotes 2. Cell Cycle (with Mitosis)-cell division in eukaryotes 3. Meiosis—cell division to form sex cells (egg and sperm)
  3. 3. Prokaryotes Divide by binary fission Circular DNA Results in two cells genetically the same What has to take place before the cells divide?
  4. 4. Eukaryotes The Cell Cycle – Growth – Repair or replacement of cells. Some cells die quickly and need to be replaced a lot (skin cells). Some cells never get replaced (nerve cells). Some organisms can regenerate whole body parts.
  5. 5.  Each cell goes through a series of phases throughout its life. The cell cycle-all events between one cell division and the next **ONE REPLICATION & ONE DIVISION 2 basic steps: Interphase (G1, S, G2) and Mitosis (M) Result? 2 daughter cells genetically exact to the parent cell they came from.
  6. 6.  First stage in Interphase G=gap Newly formed cell will go through intense growth. Takes in lots of food and energy. DNA at this point is unwound and called chromatin Interphase
  7. 7.  Second stage in Interphase S=Synthesis phase. All DNA gets replicated during this phase cell has double the genetic material (92 chromosomes)
  8. 8.  Third stage in Interphase G=gap Cell grows some more. Extra organelles are being made.
  9. 9.  After Interphase (G1, S, and G2) M=Mitosis Mitosis = Nuclear division. MITOSIS IS THE DIVISION OF THE NUCLEUS DURING THE CELL CYCLE!!! There are four mitotic steps: – Prophase – Metaphase – Anaphase – Telophase.
  10. 10. Prophase Nuclear envelope will disappear. Spindle fiber forms.
  11. 11. Metaphase Chromosomes begin to line up at the equator of the cell. Spindle fibers attach to the center of each sister chromatid of the chromosome.
  12. 12. Anaphase Spindle fibers begin to pull apart sister chromatids. Each is now a chromosome Spindle breaks down after this.
  13. 13. Telophase Each side now has a full set of chromosomes. Nuclear envelope will reform.
  14. 14. Cytokinesis “Cytokinesis”—division of cytoplasm (cleaving the cell in half.) Animal cells form a “furrow.” Plant cells form a new cell wall. Formation of two, identical daughter cells with 46 chromosomes At first new cells are smaller than the originals.
  15. 15. Overall Cell Cycle Process Interphase (G1, S, G2) and Mitosis (Prophase, Metaphase, Anaphase, Telophase)  IPMAT
  16. 16. REGULATION OF CELL CYCLE Cell division controlled by certain proteins called cyclins Cancer cells don’t respond to the cyclin signals--- uncontrolled growth (tumors) Benign tumors stay intact Malignant tumors spread throughout body (metastasize)