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Chapter 5: Cell Growth and Division Section 1: The Cell Cycle The Cell Cycle A series of growth, DNA duplication, and cell division which occurs in eukaryotes. Divided into 2 Major Parts – Interphase – Mitosis Interphase The majority of a cell’s life. Three parts of interphase: 1. Gap 1 (G1): – Normal cell functions / increase in size and number of organelles – Most of a cell’s life – A signal must be accepted telling the cell it’s ready to continue to the next stage. A “checkpoint” Interphase Continued 2. Synthesis (S): The cell duplicates its DNA. Readies itself for cell division. 3. Gap 2 (G2): Continued growth and normal functioning Another checkpoint before continuing Mitosis Two processes: 1. Mitosis: the division of the nuclei to form 2 new identical nuclei. 2. Cytokinesis: the division of the cytoplasm to form 2 identical daughter cells. Cell Cycle Rates The length of the G1 stage is different for different cells: Children: Short G1; cells are needed to grow the organs and body larger. Skin and Intestinal Lining: Short G1; need to replace cells. Nerve Cells: Never divide after a certain point. – “Stuck” in a G0 stage S, G2, and Mitosis take about 12 hours. Cell Size A cell’s size is limited to a ratio of surface area to volume. – As a cell increases in size, volume increases faster then volume. – Not enough surface area to provide adequate exchange with the environment.
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