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Chapter 10 Cell Growth & Division 1 10 –1 Cell Growth • Which has larger cells: an adult elephant or a baby elephant? • Neither! They are the same size. The adult just has more cells. 2 3 Division of the Cell • Cell divides into 2 new daughter cells. • DNA replication occurs before division 4 5 10–2 Cell Division • Every cell must first copy its genetic information before cell division begins. – Each daughter cell then gets a complete copy of that information. • Eukaryotes are more complex than Prokaryotes. In Eukaryotes: – The first stage, division of the cell nucleus, is called mitosis. – The second stage, division of the cytoplasm, is called cytokinesis. 6 Chromosomes • Genetic information is passed on from one generation of cells to the next • Chromosomes – made up of DNA and proteins • Every organism has a specific number of chromosomes – fruit flies = 8 chromosomes – humans = 46 chromosomes – carrot = 18 chromosomes 7 8 9 Chromosomes (cont.) • Chromosomes not visible except during cell division…otherwise the DNA and proteins are spread throughout the nucleus. • At beginning of cell division, chromosomes condense and are visible. • Before cell division, each chromosome is duplicated. 10 Parts of the Chromosome • chromatids – sister chromatids: each chromosome consists of 2 identical sister chromatids. (separated during cell division) • centromere – where each pair of chromatids is attached near center • Entering cell division in humans = 46 chromosomes each with sister chromatids. 11 12 The Cell Cycle • Recurring events in the life of the cell. • The series of events that cells go through as they grow and divide • During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells, each of which then begins the cycle again. 13 The Cell Cycle 14 4 Phases of the Cell Cycle • • • • G1 S G2 M G1 = intense growth and activity S = Chromosome replication G2 = intense growth and activity [Interphase = G1, S, G2 ] M = Mitosis (nucleus division) and cytokinesis (cytoplasm division) 15 16 The Cell Cycle Animation • http://www.cellsalive.com/cell_cycle.htm 17 Events of the Cell Cycle • G1 = cells do most of their growing. • During this phase, cells increase in size and synthesize new proteins and organelles. • S = chromosomes are replicated • synthesis of DNA molecules • Key proteins associated with the chromosomes are also synthesized • G2 = shortest phase of interphase • organelles and molecules required for cell division are produced 18 Mitosis • 4 phases: [P M A T] – Prophase – Metaphase – Anaphase – Telophase • Lasts from a few minutes to several days 19 Prophase • Longest phase of mitosis (50 to 60 percent of the total time of Mitosis) • Chromosomes become visible • Centrioles separate – go to opposite ends of the cell • Condensed chromosomes become attached to fibers in the spindle at a point near the centromere of each chromatid 20 Prophase (cont.) • Nucleolus disappears • Nuclear envelope breaks down • Chromosomes coil more tightly 21 Early prophase Mid prophase Late prophase 22 Metaphase • Lasts only a few minutes • The chromosomes line up across the center of the cell • Microtubules (spindle fibers) connect the centromere of each chromosome to the two poles of the spindle 23 24 Anaphase • The centromeres split • Sister chromatids separate become individual chromosomes • Chromosomes continue until they have separated into two groups near the poles of the spindle • Anaphase ends when the chromosomes stop moving 25 26 Telophase • Chromosomes begin to uncoil into a tangle of dense material • A nuclear envelope re-forms around each cluster of chromosomes • The spindle begins to break apart • A nucleolus becomes visible in each daughter nucleus 27 28 29 Mitosis Animation • http://www.cellsalive.com/mitosis.htm 30 Cytokinesis • Two nuclei — each with a full set of chromosomes — are formed, within the cytoplasm of a single cell • The division of the cytoplasm itself • Occurs at the same time as telophase 31 Animal Cells vs. Plant Cells • animal cells = cell membrane is drawn inward until the cytoplasm is pinched into two nearly equal parts • plants = the cell plate forms midway between the divided nuclei – The cell plate gradually develops into a separating membrane. – A cell wall then begins to appear in the cell plate. 32 33 34 10-3 Regulating the Cell Cycle • Controls on Cell Division – When cells come into contact with each other, cells respond by stopping growth (petri dish) – when put with space between cells, cells begin growing once again. – controls on cell growth can be turned on and off 35 Contact Inhibition 36 In the body Cut the skin or break a bone • Cells at the edges of the injury are stimulated to divide rapidly. • Produce new cells • When the healing process nears completion, the rate of cell division slows down 37 Uncontrolled Cell Growth • Cancer cells do not respond to the signals that regulate the growth of most cells • Divide uncontrollably • Form masses of cells called tumors • May break loose from tumors and spread throughout the body 38 Causes of cancer • smoking tobacco • radiation exposure • even viral infection 39 Why does cancer occur? Many cancers have a defect in a gene called p53 • p53 normally halts the cell cycle until all chromosomes have been properly replicated • Damaged or defective p53 genes cause the cells to lose the information needed to respond to signals that would normally control their growth 40 41