Cell division allows organisms to grow and reproduce. All cells come from preexisting cells through asexual or sexual reproduction. In eukaryotic cells, DNA is contained in chromosomes that condense and duplicate before the cell divides. The cell cycle consists of interphase and mitosis, where the cell makes copies of its contents and divides into two daughter cells through cytokinesis. Precise control mechanisms regulate cell division, but errors can lead to uncontrolled growth and cancer.

1. Cell Division

2. Cellular Reproduction Organism’s life begins as one cell Rudolf Virchow (1858) stated: All cells come from cells Prokaryotes divide only to reproduce Asexual repro: 1 parent  2 daughters AKA Binary fission (“dividing in half”) One set of DNA duplicates, cell divides

3. Eukaryotic cells divide for reproduction, growth, and replacement of cells Other organisms (plants & animals especially) reproduce through sexual reproduction Sperm + Egg  offspring Offspring gets two sets of genetic information, one from each parent

4. The Chromosome DNA is contained in structures called chromosomes within the nucleus of the cell “chroma” color, “soma” body Most of the time, chromatin fills the nucleus Tangled mass of fibers of DNA & protein When a cell begins to divide, the chromatin condenses and coils into chromosomes Each chromosome has one long DNA molecule containing thousands of genes

6. The Chromosome Before a cell divides, it must duplicate its chromosomes DNA replication! Once duplicated, the chromosomes have sister chromatids with identical genes, joined at a centromere When the cell divides, half goes to each daughter cell

8. The Cell Cycle Sequence of events from the time a cell divides to when it forms two daughter cells Serves to double the cell’s parts, then splits Stages: Interphase 90% Mitotic phase 10%

10. Mitotic Phase Unique to eukaryotes Ends with 2 identical cells Sub-stages of Mitosis: Prophase Metaphase Anaphase Telophase Cytokenisis

11. Prophase Sister chromatids are attached at centromere Centrioles separate and extend spindle fibers Nucleolus disappears and nuclear envelope breaks down Kinetochores form on each chromatid, spindle fibers attach

14. Metaphase Centrosomes at poles Chromosomes lined up at metaphase plate (cell’s equator) Kinetochores of sister chromatids face opposite poles

16. Anaphase Spindle fibers pull sister chromatids apart forming daughter chromosomes Chromosomes move centromere first towards opposite poles Cell elongates

18. Telophase & Cytokenisis Cell continues to elongate Daughter nuclei appear at poles Nuclear envelopes reform Spindle fibers disappear Cytoplasms separate, new cell membranes form

20. Cytokenisis Cell pinches into two cells Called a cleavage furrow Plants are a little different Vesicles save materials from cell wall Form a plate at center of dividing cell Cell plate fuses to cell wall, 2 cells

27. Factors that Affect Cell Division Most reasons are unknown “Growth Factors” Proteins need for division; if not present it stops Cell-cycle control system A system of proteins in the cell that trigger & coordinates major events in the cell cycle Make checkpoints

28. Factors that Affect Cell Division Anchorage dependence Cells must be in contact with a solid surface Density-dependant inhibition Division will slow as the population grows more dense

29. When It All Goes Wrong Cell-cycle control system malfunctions Cells divide excessively and in the wrong places; creates tumors Benign: normal cells Malignant: cancerous, invasive Will divide indefinitely if not treated

30. When It All Goes Wrong Types of Cancers Carcinoma Skin, stomach lining Sarcoma Supporting tissues, bones Leukemia & Lymphoma Blood producing tissues, bone marrow Treatments Aim to stop the spread of cancerous cells by stopping division Chemotherapy (meds) and/or Radiation