Chap 12 PPT - CHAPTER TWELVE The Cell Cycle The Key Roles...

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Unformatted text preview: CHAPTER TWELVE The Cell Cycle The Key Roles of Cell Division • The ability of organisms to reproduce best distinguishes living things from nonliving matter • The continuity of life is based on the reproduction of cells, or cell division • In unicellular organisms, division of one cell reproduces the entire organism • Multicellular organisms depend on cell division for: – Development from a fertilized cell – Growth – Repair Binary Fission • Prokaryotes (bacteria and archaea) reproduce by a type of cell division called binary fission • In binary fission, the chromosome replicates (beginning at the origin of replication ), and the two daughter chromosomes actively move apart Origin of replication Two copies of origin E. coli cell Bacterial chromosome Plasma membrane Cell wall Origin Origin 100 µm 200 µm 20 µm (a) Reproduction (b) Growth and development (c) Tissue renewal Cell division (mitosis) results in genetically identical daughter cells • Most cell division results in daughter cells with identical genetic information, DNA • A special type of division produces non- identical daughter cells (gametes, or sperm and egg cells) Cellular Organization of the Genetic Material • All the DNA in a cell constitutes the cell’s genome • DNA molecules in a cell are packaged into chromosomes • Eukaryotic chromosomes consist of chromatin , a complex of DNA and protein that condenses during cell division 20 µm • Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus • Somatic cells (nonreproductive cells) have two sets of chromosomes – diploid • Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells - haploid Chromosomes during Cell Division • In preparation for cell division, DNA is replicated and the chromosomes condense • Each duplicated chromosome has two sister chromatids , which separate during cell division • The centromere is, where the two chromatids are most closely attached 0.5 µm Chromosomes Chromosome duplication (including DNA synthesis) Chromo- some arm Centromere Sister chromatids DNA molecules Separation of sister chromatids Centromere Sister chromatids One chromatid is the original chromosome the other is the replicated chromosome • Eukaryotic cell division consists of: – Mitosis , the division of the nucleus – Cytokinesis , the division of the cytoplasm • Gametes are produced by a variation of cell division called meiosis •...
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This note was uploaded on 09/14/2011 for the course BIOL 2301 taught by Professor Staff during the Spring '11 term at Lone Star College System.

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Chap 12 PPT - CHAPTER TWELVE The Cell Cycle The Key Roles...

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