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CELL DIVISION © 2006 Mesoblast Limited www.mesoblast.com © 2007 Paul Billiet ODWS Think Of how many cells are you composed? When an organism grows bigger, do you get more cells or just bigger cells or both? When do your cells divide the fastest? Slowest? Do cells ever stop dividing? Are all cells capable of division and replacement? http://www.nobel.se/medicine/laureates/2001/press.html Cell division is a fundamental process All cells come from pre-existing cells It is necessary to replace worn out /damaged cells in multicellular organisms It is required for growth in multicellular organisms It is necessary for reproduction in unicellular or multicellular organisms © 2007 Paul Billiet ODWS Cell division replaces worn out/ damaged cells All cells die after a certain number of divisions – apoptosis. At any time some cells are dividing and some cells are dying. Childhood – Cell division > cell death Adulthood – Cell division = cell death Aging – Cell division < cell death http://www.nobel.se/medicine/laureates/2001/press.html Cell division is required for growth Organisms don’t get bigger by increasing cells size. An increase in size will require an increase in surface area to volume ratio. Cell division subdivides the cytoplasm into small units (cells) surrounded by plasma membranes © 2007 Paul Billiet ODWS Cell division is required for growth Cell division is necessary for reproduction It is necessary for reproduction in unicellular or multicellular organisms. Binary fission Mitosis Meiosis © 2007 Paul Billiet ODWS Reproduction in Prokaryotes Prokaryotes have no nucleus They have a single circular chromosome Prokaryotes simply divide their cells in two by binary fission http://instruct1.cit.cornell.edu/ © 2007 Paul Billiet ODWS Reproduction in Eukaryotes Eukaryotes must divide their nucleus (and other organelles such as mitochondria) in preparation for cell division (mitosis or meiosis) Before the nucleus divides the genetic material replicates (duplicates) © 2007 Paul Billiet ODWS Mitosis Mitotic division results in genetically identical eukaryotic cells (a clone) Mitosis is the basis of asexual reproduction Results in a cell with 2 of each chromosome – diploid. © 2007 Paul Billiet ODWS © Tyler Junior College, (no commercial use allowed - contact [email protected] for permission to use) Mitosis The process of cell division that results in the production of two daughter cells from a single parent cell. The daughter cells are identical to one another and to the original parent cell. Mitosis is a stage of the cell cycle Interphase Mitosis Prophase Metaphase Anaphsase Telophase Cytokinesis Interphase – Cell prepares for division Animal Cell Cell growth Organelles duplicated More enzymes produced DNA replicates Centrioles duplicated Plant Cell Cell growth Organelles duplicated More enzymes produced DNA replicates Stages of Interphase Interphase – Cell prepares for division Animal Cell Plant Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Prophase – Cell prepares for nuclear division Animal Cell DNA packaged into chromosomes (chromosomes condense) Centrioles move to opposite ends of cell Spindle fibers form Nuclear envelope breaks down Plant Cell DNA packaged into chromosomes (chromosomes condense) Spindle fibers form Nuclear envelope breaks down Prophase – Cell prepares for nuclear division Animal Cell Plant Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Metaphase – chromosomes prepared for division Animal Cell Chromosomes line up at center of cell. Spindle fibers attach to daughter cells at centromere. Plant Cell Chromosomes line up at center of cell. Spindle fibers attach to daughter cells at centromere. Metaphase – chromosomes prepared for division Animal Cell Plant Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Anaphase – chromosomes divide Animal Cell Spindle fibers pull chromosomes apart. ½ of each chromosome (called a chromatid) moves to each daughter cell. Plant Cell Spindle fibers pull chromosomes apart. ½ of each chromosome (called a chromatid) moves to each daughter cell. Anaphase – chromosomes divide Animal Cell Plant Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Telephase – Cytoplasm starts to divide Animal Cell DNA spreads out Nuclear envelope forms around each set of chromosomes Cell membrane invaginates Plant Cell DNA spreads out Nuclear envelope forms around each set of chromosomes Cell wall forms between the 2 nuclei to form 2 daughter cells Telephase – Cytoplasm starts to divide Animal Cell Plant Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Cytokinesis – Two new cells Animal Cell Cytoplasm continues to squeeze together and pinches into 2 new cells. Each daughter cell gets half of the organelles. Plant Cell Cell plate begins to form new cell membranes between the 2 daughter cells. New cell walls form around the cell membranes. Meiosis Meiosis results in a halving of the chromosome number in preparation for fertilisation Meiosis shuffles genes in new combinations Meiosis results in genetically different cells Meiosis and fertilisation are the basis of sexual reproduction © 2007 Paul Billiet ODWS Different kinds of cells divide at different rates E. coli – 20 minutes Yeast – 2 hours Amoeba – a few days Human embryo cell – 15-20 minutes Human adult cell – 8 hours or more Frog egg cell – 30 minutes http://www.nobel.se/medicine/laureates/2001/press.html Cell cycle video Bill Nye Cell Cycle Rap Cell Cycle Rap