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CELL REPRODUCTION MITOSIS IS CELL DIVISION • GROWTH • CELL REPAIR • NOT MEIOSIS • GOAL IS TO MAKE IDENTICAL CELLS • CELLS DO NOT DIVIDE ALL THE TIME • MITOSIS IS A VERY SHORT PERIOD • MOST OF THE TIME IS INTERPHASE Genetic Control of Cell Reproduction LIFE CYCLE OF THE CELL: M phase: • mitosis • cytokinesis M (mitosis) G2 (Gap 2) G1 (Gap 1) EUKARYOTIC CELL CYCLE S phase (DNA synthesis) Interphase (>95%): • G1 phase Cells that • S phase (DNA synthesis) cease division • G2 phase DNA Replication: S phase • switched on by the cytoplasmic S-phase activator • Replication is initiated at replication origin and proceeds in both directions. • Entire genome is replicated once - further replication is blocked • involves DNA polymerase and other proteins that function to unwind and stabilize the DNA and “prime” DNA replication of the “lagging” strand. DNA Replication: S phase • nucleotides are always added to the 3’ end (DNA and RNA) • formation of Okazaki fragments on lagging strand • “new” DNA is proofread by DNA polymerase • repairs are made and gaps filled by DNA ligase Chromosomes and Their Replication • “New” DNA helices associate with histones to form chromosomes • The two chromosomes remain temporarily attached at the centromere. • Together, these chromosomes are called chromatids. •MITOSIS • REMEMBER PMAT • PROPHASE • METAPHASE • ANAPHASE • TELOPHASE •INTERPHASE • TECHNICALLY NOT PART OF MITOSIS • DNA IS COPIED (DUPLICATED) • CENTROSOMES ARE DUPLICATED •PROPHASE • CHROMOSOMES THICKEN •METAPHASE •FOR MIDDLE • ANAPHASE • ”AWAY” • CHROMOSOMES MOVE TO OPPOSITE SIDE OF THE CELL • THEY HAVE SPINDLES • TELOPHASE • FOR TWO Stages of Cell Reproduction Mitosis: M phase 1. Assembly of the mitotic apparatus 2. Prophase (A,B,C) 3. Prometaphase (D) 4. Metaphase (E) 5. Anaphase (F) 6. Telophase (G, H) Figure 3-13 • FILM Cell Differentiation Different from reproduction ... • changes in physical and functional properties of cells as they proliferate • results not from the loss of genes but from the selective repression/expression of specific genes • development occurs in large part as a result of “inductions,” one part of the body affecting another THE CELL CYCLE & CANCER • GROWING OF CELLS OUT OF CONTROL CANCER Dysregulation of cell growth Caused in all or almost all cases by the mutation or abnormal activation of genes that encode proteins that control cell growth and/or mitosis • Proto-oncogenes: the “normal” genes • Oncogenes: the “abnormal” gene • Antioncogenes: genes whose product suppress the activation of oncogenes Not all mutations lead to cancer! What causes these mutations? • Ionizing radiation: disrupts DNA strands • Chemicals: “carcinogens” • Physical irritants: e.g., abrasion of the intestinal lining • Hereditary “tendencies”: e.g., some breast cancer • Viruses: so-called “tumor viruses” (particularly retroviruses) Q: Why does cancer kill? A: Cancer cells compete successfully with normal cells for limited nutrients