Ch_5_SG_020608 - Chapter 5 Cell Division Feb 6 2008 5.1...

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Chapter 5 Cell Division Feb 6, 2008 5.1 Cell increase and decrease Increase and decrease of cell numbers Cell division increases number of somatic cells Mitosis-division of nucleus of cell Cytokinesis-division of cytoplasm Occurs throughout life; growth, development, repair Apoptosis- program cell death decreases cell no. Occurs throughout life also Prevents abnormal cells from proliferating The cell cycle Set of events that occur between the time a cell divides and the time the resulting daughter cells divide Stages of interphase –longest phase of the cycle Normal cell fns. occur as well as prepn. for division G1 stage-organelles double in number, accumulates materials needed for division S stage-DNA replication The cell cycle Mitotic stage Follows interphase Includes mitosis and cytokinesis Control of cell cycle The protein cyclin must be present for stages to progress replicating or is damaged Control of the cell cycle Apoptosis Progressive series of events resulting in cell destruction Cell rounds up, & loses contact w/ surrounding cells Nucleus breaks up and cell undergoes fragmentation Mediated by 2 sets of enzymes called caspases One set initiates the events The other set activates enzymes that digest the cell Apoptosis 5.2 Maintaining the chromosome number Maintaining the chromosome number- terminology Chromatin -tangled mass of threadlike DNA in nondividing cell Chromosomes -condensed rod-shaped DNA molecules during division Diploid (2N) number-characteristic chromosome number, chromosomes in pairs Haploid (N) number- half the diploid number, found in gametes Overview of mitosis Nuclear division where chromosome no. is constant DNA replication produces duplicated chromosomes
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Each duplicated chromosome is composed of 2 sister chromatids held together by a centromere Sister chromatids are genetically identical
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