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The Cell Cycle Mitosis & Cytokinesis Why do living things grow? • This baby king penguin grows because he produces more and more cells. How do cells know when to quit dividing? • Cell growth is CAREFULLY controlled. • Only certain cells are allowed to divide rapidly. –Ex. Hair follicles & stomach lining. •One experiment using cells in a petri dish showed that they stopped dividing when they touched! •But…… That’s not always the case… Breast cancer cell Liver Cancer cells Mitosis • The process where the nucleus divides into two new, IDENTICAL, nuclei. During the early stages of Mitosis… • The chromatin (DNA + Proteins) becomes condensed (gets tighter) and you can see the chromosomes. Chromosomes • Chromosomes are tightly coiled chromatin/DNA. A Chromosome *Two sister CHROMATIDS Make up the chromosome *The CENTROMERE, a sticky Spot in the middle of the Chromosome, keeps the sister Chromatids together. Interphase • A long period between cell divisions. • Doubling of all cell parts happens. • Most cells, when looked at under the microscope are in interphase because it takes the longest time. M I T O S I S Mitosis is… •The process of cell growth & division . • There are 4 parts of Mitosis: –P –M –A –T Prophase Metaphase Anaphase Telophase Prophase Interphase Anaphase Telophase Interphase • This cell shows how all cells look before mitosis. • Interphase is a phase of the cell cycle, but NOT a stage of mitosis. Prophase • The nuclear membrane breaks down. • The chromosomes become visible (shorten and thicken). • The other structures important for mitosis are also forming (ex. the centrioles). Metaphase *The chromosomes are pulled to the cell's equator by the spindle fibers. *The chromosomes MEET IN THE MIDDLE Anaphase • The newly formed chromosomes are pulled by the spindle fibers, AWAY from each other, toward opposite poles of the cell. Telophase • The chromosomes stop moving. • The spindle fibers break down. • The membrane of the cell pinches creating two separate cells. • The nuclear membrane reforms. • The nucleolus reappears. Very Last Part… Cytokinesis • This is when the two new cells completely divide. • Plant and animal cells do this differently! Animal Cell • A ring (contractile ring) tightens and tightens until the two new cells pinch apart. Furrow Plant Cell • A cell plate forms between the two cells and this forms into the cell wall eventually.
