CHAPTER8 - Chapter 8 Cell Reproduction I Introduction A...

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Chapter 8: Cell Reproduction I. Introduction A. Prokaryotic cells will increase in number by undergoing binary fission 1. Form of asexual reproduction 2. The two daughter cells produced are genetically identical B. Eukaryotic cells 1. Body cells = Somatic cells a. Form a functioning part of the body b. Divide by the process of Mitosis c. Purpose - growth, repair, and maintenance 2. Sex cells = Gametes a. Found in the reproductive organs b. Divide by the process of Meiosis c. Purpose - instead of becoming a part of the organism, these cells will form a completely new organism by uniting through the process of sexual reproduction II. Chromosomes A. Structures within the nucleus that contain the genetic information ( DNA ) that is passed on from one generation of cell to another B. Somatic cells of every organism contain a specific number of chromosomes 1. Each chromosome occurs as a member of a pair (= homologous chromosomes ) 2. Human somatic cells have 46 chromosomes or 23 pairs a. One chromosome of the pair comes from the father and the other comes from the mother b. A cell with chromosomes occurring in pairs is called Diploid or 2n C. Gametes 1. Cannot be diploid or else the resulting zygote (fertilized egg) would contain twice as many chromosomes as it should 2. Because of meiosis, the gametes contain only one chromosome of each pair and are said to be Haploid or 1n D. Each chromosome is a molecule of DNA complexed with proteins E. Prior to division, each thread-like chromosome is duplicated to form two sister chromatids held together by a centromere III. Somatic Cell Cycle A. Period of time from the beginning of one division to the beginning of the next division B. Interphase 1. Gap 1 or G1 phase a. Period when the cell grows b. Enzymes need for next phase are synthesized 2. Synthesis or s phase - period of DNA replication a. An enzyme, DNA Helicase, recognizes a DNA double helix b. It attaches and causes the double helix to unwind
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Chapter 8 page 2 c. The enzyme, DNA Polymerase, then travels along the two opened strands in opposite directions d. As it travels, it matches up free nucleotides from the nucleoplasm with the existing nucleotides e. Pattern of matching is specific: 1. Adenine always pairs with Thymine 2. Cytosine always pairs with Guanine f. When the enzymes reach the ends, they release the strands and the end result is two DNA double helices g. The result is the two sister chromatids are genetically identical 3. Gap2 or G2 phase a. In animal cells, the centrioles and spindle fibers are synthesized b. In plant cells, only spindle fibers are synthesized C. Mitosis - Division of the Nucleus 1. Prophase a. Chromatin condenses and becomes visible as replicated chromosomes
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