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Cell Division and Mitosis Starr/Taggart’s Biology: The Unity and Diversity of Life, Chapter 9 9e Key Concepts: Continuity of life depends on reproduction After cell division, each daughter cell must receive the same amount of DNA The cell cycle: Interphase and Mitosis DNA and proteins make up chromosomes in eukaryotic cells Members of the same species have the same number of chromosomes in their cells Key Concepts: The body cells of many organisms have a diploid chromosome number Mitosis keeps the chromosome number constant Mitosis is the basis of growth and tissue repair in multicelled eukaryotes. Single-celled eukaryotes and many multicelled eukaryotes reproduce by mitosis Overview DNA contains hereditary instructions Before cells reproduce, they must undergo nuclear division Mitosis Meiosis Multicelled organisms grow and repair themselves by mitosis Overview Mitosis and meiosis are nuclear division mechanisms Mitosis in somatic cells allows growth, repair, and asexual reproduction Meiosis occurs in germ cells, produces gametes, allows sexual reproduction Prokaryotic cells reproduce asexually Chromosomes Each chromosome duplicates in preparation for mitosis Sister chromatids remain attached Mitosis and Chromosome Number Chromosome number = Total of chromosomes in somatic cells Humans 46 Gorillas 48 Pea plants 14 Chromosomes are in pairs Humans 23 pairs 2n “diploid” 1n “haploid” (gametes) The Cell Cycle A diploid cell produces two diploid daughter cells Two phases in cell cycle Interphase Longest phase Increase in mass, doubles components, and duplicates DNA Mitosis Nuclear division Interphase G1 “Gap” - cell growth before DNA replication S “Synthesis” - DNA replication G2 “Second Gap” - preparation for division The length of each part differs among different cell types The Cell Cycle Mitosis Four stages Prophase Metaphase Anaphase Telophase Cytokinesis Cytoplasmic division Prophase Chromosomes become visible Spindle apparatus forms Centrioles move apart to opposite poles Microtubules break apart into tubulin subunits New tubulin subunits form the spindle Nuclear envelope breaks up Prophase Metaphase Chromosomes interact with microtubules on spindle apparatus Attachment at centromeres • Kinetochore Tubules pull on chromosomes Orientation of sister chromatids to opposite poles Alignment of chromosomes midway between the poles Metaphase Anaphase Separation of sister chromatids Movement toward opposite poles Separation of Sister Chromatids Microtubules attached to centromeres shorten and pull chromosomes towards poles Separation of Sister Chromatids Spindle elongates and the spindle poles are pushed farther apart by overlapping microtubules Telophase Chromosomes arrive at spindle poles Chromosomes return to threadlike forms New nuclear membranes form Two nuclei form Cytokinesis Division of cytoplasm Forms two cells Metaphase to Interphase Cytoplasmic Division Cytokinesis Between late anaphase and end of telophase In plants: cell plate forms Vesicles fuse In animals: cleavage Cleavage furrow - depression forms at cell’s midsection In Conclusion A parent cell provides each daughter cell with hereditary instructions Eukaryotes divide by mitosis or meiosis and prokaryotes divide by binary fission Each chromosome is one DNA molecule with proteins attached Cells with a diploid number (2n) contain two of each kind of chromosome In Conclusion Mitosis maintains the chromosome number from one cell generation to the next Mitosis is the basis of growth and tissue repair, and asexual reproduction in some eukaryotes The cell cycle includes interphase and mitosis The phases of mitosis are prophase, metaphase, anaphase, and telophase developed by M. Roig