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AP Biology 2007-2008 Biology is the only subject in which multiplication is the same thing as division…
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AP Biology Uses of Mitosis Growth Organisms grow by increasing number of cells, not cell size. Think surface-area to volume ratio. Tissue Repair: w ounds close by creating cells identical to those that were lost or injured. Embryonic Growth: increasing cell number Asexual Reproduction (Binary Fission)
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AP Biology Stages of the Cell Cycle Mitotic Phase Refers to the process of nuclear division Cytokinesis The actual physical division of the cell Not included in the mitotic phase Division of the cytoplasm and its contents Interphase
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AP Biology Life Cycle of Cell cell is formed from a mitotic division cell grows & matures to divide again cell grows & matures to never divide again G 1, S, G 2, M G1G0G1G0 epithelial cells, blood cells, stem cells brain / nerve cells muscle cells liver cells
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AP Biology Interphase (longest stage of cell’s life) Divided into 3 phases: G 1 = 1 st Gap Cell doing its “everyday job.” Cell grows. S = DNA Synthesis Copies chromosomes. G 2 = 2 nd Gap Prepares for division. Cell grows (more). Produces organelles, proteins, membranes. G0G0 signal to divide
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AP Biology S-Phase of Interphase Dividing cell replicates DNA Must separate DNA copies correctly to 2 daughter cells. Human cell duplicates ~3 meters DNA. Each daughter cell gets complete identical copy. Error rate = ~1 per 100 million bases 3 billion base pairs in mammalian genome. ~30 errors per cell cycle Mutations (to somatic cells).
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AP Biology Organizing DNA DNA is organized in chromosomes Double helix DNA molecule Wrapped around histone proteins DNA-protein complex = chromatin Organized into long thin fiber. Condensed further during mitosis (prophase). ACTGGTCAGGCAATGTC After DNA duplication, chromatin condenses.
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AP Biology Mitotic Chromosome Duplicated chromosome 2 sister chromatids. Narrow at centromeres. Contain identical copies of original DNA.
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AP Biology G1, S, and G2 of interphase used to be called the “resting phase.” Why is resting phase not a good name?
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AP Biology Prophase Nucleoli disappear. Nuclear membrane breaks down. Each duplicated chromosome appears as two identical sister chromatids joined at centromere. Visible in light microscope. Mitotic spindle forms. Centrosome Radiating microtubules Centrosomes move away from each other.
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AP Biology Prometaphase: Transition to Metaphase Chromosomes attach to microtubules. At kinetochore. Each chromosome is oriented such that the kinetochores of sister chromatids are attached to microtubules at opposite poles. Chromosomes begin moving to the middle.
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AP Biology Metaphase All chromosomes are aligned at equator of the cell, called the metaphase plate. Chromosomes are attached to opposite poles and are under tension. Helps to ensure chromosomes separate properly. Ensures each new nucleus receives only ONE copy of each chromosome.
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AP Biology Anaphase Cohesion proteins (hold sister chromatids together) cleaved by separase. Kinetochore microtubules shorten. Motor proteins assist. Sister chromatids pulled to opposite sides of the cell. Non-kinetochore microtubules lengthen and elongate cell.
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AP Biology Telophase Sister chromatids arrive at opposite poles. Spindle disappears. Centrioles replicate (in animal cells. Nuclear membrane reappears. Nucleolus becomes visible. Chromosomes become chromatin (uncoiling).
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AP Biology Cytokinesis Animals Cleavage furrow forms. Splits cell in two. A belt of actin pinches off daughter cells. Plants Cell plate forms. Vesicles line up at equator and fuse. https://www.youtube.com/watch?v=aDAw2Zg4IgE https://www.youtube.com/watch?v=pOsAbTi9tHw
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