CELL DIVISION Mitosis and Meiosis Why do cells have to divide? • • Demonstration 3 reasons cells must divide 1) Replace damaged or dead cells 2) Growth 3) Surface area to volume ratio What is cell division? • Cells replicate themselves • Rates of division 1) Bacteria: 20 minutes What is cell division? (cont.) • Rates (cont) 2) Average body cell (ex: lining of esophagus, or skin cells): about 24 hours Rates of Division (cont.) 3) Red Blood Cells- Do not divide, but has a life span of about 180 days. Made in the bone marrow. Rates of Division (cont.) 4) Nerve cells= Do not divide The Cell Cycle 2 main parts of the cell cycle: 1) Interphase 2) Mitosis Part 1: Interphase • G1 = The cell grows, doubles in size, and doubles the number of organelles • S = Synthesis of DNA, replication of DNA happens • G2 = Second growth phase, prepares for division Part 2: Mitosis • The cell divides by going through the following phases: • P. M. A. T. Then cytokinesis • P= Prophase • M= Metaphase • A= Anaphase • T= Telophase Interphase (before mitosis) • DNA is copied. The two sets of DNA are condensed into Chromosomes that are connected at the center (the centromere). These are known as “sister chromatids” Prophase • Cell division begins. Centrioles form at either end of the cell and begin to form spindle fibers Centriole Metaphase • Sister chromatids attach to the spindle fibers Centriole Anaphase • Sister chromatids separate and begin to move towards the centrioles at either end of the cell. Telophase • The separate chromatids are surrounded by a new nuclear membrane forming a new nucleus with a complete set of DNA. Cytokinesis • The cell membrane moves inward to create two new cells.