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Bell Ringer 1. Why do cells need to divide in multicellular organisms? 2. What is the difference between prokaryotes and eukaryotes with regard to chromosomes? 3. What does a human chromosome consist of? Draw one! Label. 4. Describe a role of chromatin in chromosome in your own words. DNA and Chromosomes Chromatin DN A The function of chromatin is to efficiently package DNA Histones Cell Cycle Cell Cycle is a sequence of events through which a cell progresses during its lifetime • Cell can be either in dividing (Mitotic Phase) or non-dividing state (Interphase) Interphase about 90% of the cell cycle G1 Phase (Gap 1): • • • • Cell Growth Protein Synthesis Cell Metabolism Preparation for S Phase S Phase (synthesis): – DNA is replicated G2 Phase (Gap 2): • Further Cell Growth • Protein Synthesis • Specialized proteins needed for Cell Division The cell grows during all three phases, but chromosomes are duplicated only during the S phase Mitotic Phase Mitosis: • • • • Prophase Metaphase Anaphase Telophase Cytokinesis is division of cytoplasm/cell: – cleavage furrow forms in animal cells – cell plate (cell wall) forms in plant cells – daughter cells are identical Figure 12.10a (a) Cleavage of an animal cell (SEM) Cleavage furrow Contractile ring of microfilaments 100 m Daughter cells Figure 12.10b (b) Cell plate formation in a plant cell (TEM) Vesicles Wall of parent cell forming cell plate Cell plate 1 m New cell wall Daughter cells Cell Cycle • Interphase • Prophase • Metaphase • Anaphase • Telophase & Cytokinesis Interphase Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Plant Cell Prophase Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Plant Cell Prophase The cell prepares for nuclear division • Animal and Plant Cell – Packages DNA into chromosomes – nuclear envelope breaks down – Centrosomes move apart and forms spindle which guides chr. separation Metaphase Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Plant Cell Metaphase The cell prepares chromosomes for division • Animal and Plant Cell – Chromosomes line up at the center of the cell – Spindle fibers attach from daughter cells to chromosomes at the centromere Anaphase Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Plant Cell Anaphase The chromosomes divide • Animal and Animal Cell – Spindle fibers pull chromosomes apart – ½ of each chromosome (called chromotid) moves to each daughter cell Telophase Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Plant Cell Telophase The cytoplasm divides • Animal Cell – – – – – chromosomes uncoil 2 nuclei form spindle breaks down nuclear envelope and nucleoli reappear