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k THE CELL CYCLE Overview • Complex process • Eukaryotic cells • All cells divide at different rates (muscles v skin) • Must replicate perfectly for – Growth – Repair Overview • Creates two identical daughter cells from a parent cell (46 chromosomes each) • Happens in body cells (somatic cells) 3 Distinct Periods • Interphase • Mitosis • Cytokinesis Description of Each Stage • Interphase • Longest Stage • Three Phases – G1 = cell growth and development/ doing it job – S = DNA replicates – G2 = additional growth – Genetic Material now in chromatin form DNA Chromosome • Start w/ DNA • Wind around histones • Condenses to form chromatin • Chromatin condenses to form chromosomes – Made of two sister chromatids Labeled Chromosome Mitosis • 4 Phases – – – – Prophase Metaphase Anaphase Telophase * Must know what is happening with the chromosomes at each phase Animated Mitosis Cycle http://www.cellsalive.com/mitosis.htm Animal Cell Plant Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Prophase Details Prophase • Chromatin condenses and becomes visible = chromosomes • Nuclear membrane dissolves • Spindle fibers form • Centrioles separate Animal Cell Plant Cell Spindle fibers Centrioles Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Metaphase Details • Chromosomes line up down center of cell • Attach to spindle fibers Animal Cell Plant Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Anaphase Details • Sister chromatids separate • Spindle fibers shorten to move chromatids to opposite sides of cell Animal Cell Plant Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Telophase Details • Chromosomes are now split and in two almost new nuclei • Chromosomes uncoil to chromatin • Nuclear envelope reforms • Fibers disappear Animal Cell Plant Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Cytokinesis • The cytoplasm splits and 2 new cells are formed • Daughter cells IDENTICAL to original Meiosis • A double division to produce sex cells with half the number of chromosomes- one copy of each gene • Mixes genes through independent assortment and crossing over to gain variety! • Humans-23 chromosomes in each egg or sperm cell (gamete) Independent Assortment- Crossing Over “Putting It All Together” - Fertilization Mitosis Number of divisions Number of daughter cells Genetically identical? Chromosome # Where When Role Meiosis Using the above example as a layout-Create a neat chart showing the differences between mitosis and meiosis. Mitosis Meiosis 2 Number of divisions 1 Number of daughter cells 2 4 Yes No Same as parent Half of parent Where Somatic cells Germ cells- gametes When Throughout life At sexual maturity Growth and repair Sexual reproduction Genetically identical? Chromosome # Role
