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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 and cell division are CAREFULLY controlled. • Only certain cells are allowed to divide rapidly. –Ex. Hair follicles & stomach lining. Experiment on Cell Growth •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 SCARS-why do they look different? • Scar Tissue is not of the same quality as unscarred skin. • It is less capable of resisting ultraviolet radiation. • It will not regrow hair follicles. • It will not regrow sweat glands. Mitosis • The process where the nucleus is divided into two new, IDENTICAL, nuclei. During the early stages of Mitosis… •The chromatin (DNA + Proteins) becomes condensed and you can see the chromosomes. Supercoiling cont. Histones- Special proteins the DNA coils around. Nucleosomes- A coiled, beadlike structure of DNA wrapped around a histone. Chromosomes • Chromosomes contain highly supercoiled strands of DNA. p. 225 in your book shows supercoiling 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. The Cell CycleI,P,M,A,T & Cytokinesis •Read pages228-229 •Write down what parts make up the cell cycle. Interphase p. 228 • A long period between cell divisions. • 3 phases G1, S, G2 –G1, Cell grows –S, DNA doubles –G2, Organelles double
