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Cell Division needed for Growth and Repair Mitosis • • • • • Produces genetically identical cells DNA replicates in parent cell Cell divides to produce 2 new cells Each with exact copy of parent DNA Variation only if a mutation occurs The Cell Cycle Cytokinesis:cytoplasm divides Nucleus divides growth new protein and organelles made mitosis G1 Proteins needed for cell division made G2 S DNA replicates Amount of DNA during the cell cycle S phase Mitosis Interphase Cytokinesis Interphase nucleolus chromatin threads nuclear membrane centrioles Interphase Prophase Chromosomes shorten and thicken becoming visible CONDENSATION Nuclear envelope breaks down Nucleolus breaks down Centrioles duplicate Prophase Centrioles move to opposite poles of the cell Centrioles start to produce spindle fibres early prophase prophase Metaphase Chromosomes line up at the equator Chromosomes are attached to the spindle by the centromere metaphase Anaphase Spindle fibres contract pulling the sister chromatids apart Anaphase Spindle fibres contract pulling the sister chromatids apart Anaphase Chromatids approach the poles Anaphase Late anaphase Telophase Chromatids reach opposite poles. At the poles they are called chromosomes Telophase Nuclear membrane begins to form around each set of chromosomes Spindle breaks down Telophase Constriction of the cytoplasm begins to separate the cells CYTOPLASMIC CLEAVAGE or CYTOKINESIS Telophase Cytokinesis Membrane divides the cells Cell walls are formed in plants and fungi Cytokinesis Chromosomes become long and thin Chromosomes are indistinct CHROMATIN Nucleolus reappears Cytokinesis in a plant cell Cells enter interphase They grow Copy DNA Replicate organelles Ready to divide Why mitosis is important • Growth - each new cell is identical to the parent cell, CLONE • Repair - replace damaged cells, e.g. red cells are replaced about every 3months • Asexual reproduction - Single celled organisms divide to produce two daughter cells Budding in yeast
