The Cell Cycle

The Cell Cycle - The Cell Cycle-Mitosis and Cytokinesis 1 2...

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The Cell Cycle—Mitosis and Cytokinesis 1 The ability of organisms to reproduce their kind is the one characteristic that best distinguishes living things from nonliving matter. 2 The continuity of life is based on the reproduction of cells, or cell division. A. The Key Roles of Cell Division 1. Cell division functions in reproduction, growth, and repair. 1 The division of a unicellular organism reproduces an entire organism, increasing the population. 2 Cell division on a larger scale can produce progeny for some multicellular organisms. 3 This includes organisms that can grow by cuttings. 4 Cell division enables a multicellular organism to develop from a single fertilized egg or zygote. 5 In a multicellular organism, cell division functions to repair and renew cells that die from normal wear and tear or accidents. 6 Cell division is part of the cell cycle, the life of a cell from its origin in the division of a parent cell until its own division into two. 2. Cell division results in genetically identical daughter cells. 1 Cell division requires the distribution of identical genetic material—DNA—to two daughter cells. 2 What is remarkable is the fidelity with which DNA is passed along, without dilution, from one generation to the next. 3 A dividing cell duplicates its DNA, allocates the two copies to opposite ends of the cell, and then splits into two daughter cells. 4 A cell’s genetic information, packaged as DNA, is called its genome. 5 In prokaryotes, the genome is often a single long DNA molecule. 6 In eukaryotes, the genome consists of several DNA molecules. 7 A human cell must duplicate about 2 m of DNA and separate the two copies such that each daughter cell ends up with a complete genome. 8 DNA molecules are packaged into chromosomes. 9 Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus.
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: Human somatic cells (body cells) have 46 chromosomes, made up of two sets of 23 (one from each parent). : Human gametes (sperm or eggs) have one set of 23 chromosomes, half the number in a somatic cell. 10 Eukaryotic chromosomes are made of chromatin, a complex of DNA and associated protein. 11 Each single chromosome contains one long, linear DNA molecule carrying hundreds or thousands of genes, the units that specify an organism’s inherited traits. 12 The associated proteins maintain the structure of the chromosome and help control gene activity. 13 When a cell is not dividing, each chromosome is in the form of a long, thin chromatin fiber. 14 Before cell division, chromatin condenses, coiling and folding to make a smaller package. 15 Each duplicated chromosome consists of two sister chromatids, which contain identical copies of the chromosome’s DNA. 16
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The Cell Cycle - The Cell Cycle-Mitosis and Cytokinesis 1 2...

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