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Transcript
THE CELL CYCLE, AND CELL DIVISION 1. 2. 3. Objectives: Describe the life cycle of a cell (explain what happens in each phase of the life cycle) Describe the process of mitosis and state its function Explain the role that mitosis plays in transmitting genes from one cell to the next. Why Do Cells Divide? • Unicellular organisms use cell division primarily for reproduction. • In multicellular organisms, cell division is also important in growth and repair of tissues. Figure 9.1 Important Consequences of Cell Division The cell cycle: Events that occur to produce two eukaryotic cells from one. (eukaryotic cells have nuclei) Interphase A period between divisions, when the cell grows rapidly and prepares for mitosis by copying its DNA Most of the life of a cell is spent in interphase Mitosis Cell division The Eukaryotic Cell Cycle Four events must occur for cell division: • Reproductive Signal: to initiate cell division • Replication: of DNA • Segregation: distribution of the DNA into the two new cells • Cytokinesis: separation of the two new cells Prokaryotic Cell Division Figure 9.2 Prokaryotic Cell Division (Part 2) Eukaryotic Cells Division: • Eukaryotes usually have many chromosomes. • Mitosis is the process that segregates the chromosomes. • The nucleus must be divided into two nuclei before the cell can split into daughter cells 9.3 What Happens during Mitosis? Mitosis can be divided into phases: • Prophase • Metaphase • Anaphase • Telophase The cell enters mitosis from interphase Interphase - each chromosome copies itself to make sister chromatids (bundles of DNA) that are held together by centromeres (proteins) - two identical chromatids joined together are called a chromosome Chromatin fibers consist of DNA and proteins The centromere is visible as a constriction. Recall DNA replication 1. Prophase MITOSIS • Nuclear membrane disappears • Chromatids (DNA coils) become visible • Centrioles move to opposite sides of cell and spindle fibers grow from the centrioles to the centromeres on each sister chromatid Prophase Spindle fibers Figure 9.10 Mitosis (Part 1) 2. Metaphase • Chromatids line up in the centre of the cell 3. Anaphase • Sister chromatids are pulled apart by the spindle fibers at the centromeres 4. Telophase • Spindle breaks down • Chromosomes uncoil • Nuclear envelope and nucleoli are reformed • Two daughter nuclei are formed with identical genetic information Figure 9.10 Mitosis (Part 2) Cytokinesis (follows mitosis) - division of the cytoplasm - cell membrane moves in to pinch off two daughter cells, each with its own nucleus with identical chromosomes Figure 9.12 Cytokinesis Differs in Animal and Plant Cells Plenary 1. A cell with 10 chromosomes undergoes mitosis. How many chromosomes would be in each of the resulting daughter cells? 2. What happens in interphase to allow the cell to be capable of undergoing future divisions? 3. What is the significance of cytokinesis? What do you think would happen if this process didn’t happen? Interphase - Onion Prophase - Onion Metaphase - Onion Anaphase - Onion Telophase - Onion Prophase - Whitefish Metaphase - Whitefish Anaphase - Whitefish Telophase – Whitefish Count ‘em Up!!!! Count the cells on the following two slides. Count the number of cells in interphase and in cell division (mitosis) For 20 Onion root tip cells cells For 20 Whitefish blastula # in Interphase # in Interphase # in Division # in Division What type of cells are these???