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Download Honors Biology Chapter 8 Mitosis Notes 3-13
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Transcript
Chapter 8: Cellular Basis of Reproduction and Inheritance Cells give rise to more cells (part of Cell Theory) Asexually reproducing organisms produce identical or nearly identical “daughter” cells to themselves. Strawberry Hydra Sexually reproducing organisms produce “daughter” cells/organisms that are much more varied. Why? Dogs Dog breeds display particular traits from a wide variety of traits found in the species. Selective breeding produces offspring that are more similar to their parents. o Less variable than the whole species Cell Division Why do cells divide? 1. Asexual reproduction for some unicellular and multicellular organisms. (Binary Fission or Mitosis) 2. Growth – multicellular organisms only (Mitosis) 3. Repair/renewal – multicellular organisms only (Mitosis) 4. Formation of sex cells: sperm and eggs (Meiosis) Prokaryotic Cell Division – Binary Fission Why don’t we call this type of division Mitosis? Bacteria reproduce asexually. The chromosome is duplicated (copied) Cell grows in size Copies are separated from each other and moved to opposite sides of cell. Plasma membrane and cell wall pinches inward to form two separate cells. Eukaryotic Cell Genetic Material and Chromosome Duplication Eukaryotic cells are generally larger than prokaryotic cells. Eukaryotic cells have many more genes than prokaryotic cells and they are located on more than one chromosome. Genetic material located in the nucleus. Genetic Material Terms: Chromatin – diffuse mass of long, thin fibers of DNA and proteins. Genetic material spends most of its time in this state. Sister Chromatids – two copies of the same DNA molecule connected by a centromere (narrow portion). Connected chromatids are identical right after duplication. Chromosomes – supercoiled, compact chromatin DNA wound around proteins. Prior to and during cell division. Visible under a light microscope, often stained. 1 = Magnified portion of a DNA molecule 2 = Less magnified portion of a DNA molecule, proteins visible 3 = Chromatin, unreplicated 4 = Replicated chromatin (made of sister chromatids) 5 = Replicated chromosome (made of sister chromatids) Cell Cycle The “life-history” of cells. Once mature, an organism maintains a fairly constant cell number. o Humans – 100 trillion cells Millions of cells dividing/sec in your body. Some divide 1/day (skin) Some less often (liver/kidney) Some not at all once mature (nerve/muscle) Cell Cycle – ordered sequence of events that starts from cell formation to cell division. Two Phases: Interphase and Mitotic phase (M phase) o Each with its own subphases Interphase – 90% of cell cycle o Perform daily function o Cell growth o Organelle/DNA doubling Subphases: o G1 (Gap phase 1) – Cell grows, doubles building blocks (?) to make more DNA. o S phase (synthesis) – Cell grows, Copies/Replicates DNA molecules o G2 (Gap phase 2) – Cell grows, doubles organelles needed for a second cell to survive. Mitotic Phase (M phase) – 10% of cell cycle o Nuclear and Cellular Division Subphases: o Mitosis – Nuclear division; nucleus and genetic material divide and reform into two nuclei with identical genetic material. Prophase Prometaphase* Metaphase Anaphase Telophase o Cytokinesis – cellular division, cytoplasm divided Mitosis is very accurate. o 1 error in 100,000 cell divisions Reorganize this diagram into a flow chart. Interphase IS NOT part of Mitosis Mitotic Phase (M phase) Mitosis and Cytokinesis Mitosis Prophase o Replicated chromatin supercoils into replicated chromosomes; Centromere visible o Nucleoli disappear o Mitotic spindle, made of microtubules, begins to form Prometaphase o Nuclear envelope breaks down o Some spindle microtubules attach to a protein structure called the kinetochore located at the centromere of each replicated chromosome o Other spindle microtubules connect to microtubules from the other centrosome Metaphase - Middle o Chromosomes line-up along the metaphase plate Imaginary plane between the poles Kinetochores face the centrosome poles Anaphase - Separate o Sister chromatids separate Pulled by microtubules to opposite poles Now each an Unreplicated Chromosome o Spindle-Spindle interactions elongate the cell Telophase – reverse prophase o Nuclear envelopes reform around genetic material o Unreplicated chromosomes uncoil to unreplicated chromatin o Nucleoli reform o Mitotic spindles fibers (microtubules) disappear Cytokinesis – Cellular Division Division of cytoplasm to both new cells Usually begins during telophase End Result: Two identical daughter cells Both identical to parent cell Possible uses: o Growth o Wound Repair/Replacement o Asexual Reproduction Animal vs. Plant Cytokinesis Animal Cells Divide from the outside-in o Cleavage furrow – groove in the cell surface caused by actin microfilaments and myosin proteins Deepens to pinch the cell into two Plant Cells Divide from the inside-out o Cell plate – vesicles containing cell wall material accumulate in the center of the cell Membranes and cell wall components fuse to form a new cell wall Growth Factors and Anchorage Organisms must be able to regulate cell division Different tissues divide at different rates in an organism o Skin and digestive tract frequently divide Anchorage Dependence – most animal cells must be in contact with a “solid surface” to divide Embryo Implantation Density-Dependent Inhibition – a single layer of cells form when grown in a Petri dish Crowded cells stop dividing o How does this relate to wound repair? Growth Factors – secreted proteins that stimulate division o Chemical cues regulate division, not physical contact o Over stimulated cells smaller and more numerous Growth factors and environmental conditions signal the CCCS (Cell Cycle Control System) o Molecules that trigger and coordinate events in the cell cycle o Stop signals prevent the cell cycle o Go-ahead signals override stop signals Tumors – Diseases of the cell cycle Benign tumors – masses of unregulated cell growth that stay in one location o Problematic based on location Transformation – normal cell changes into cancer cell o Immune system normally destroy transformed cells o Form malignant tumors Malignant tumors - Cancer o Cancer cells do not respond normally to the cell cycle control system o Divide uncontrollably No density-dependent inhibition Don’t need growth factors Some produce their own growth factors “Immortal” – divide indefinitely (normal <50X) o Invade other tissues – metastasis o Recruit new blood vessels to “feed” cells Cancers named based on the organ or tissue from which they originated (Not Tested) o Carcinomas – originate from external/internal covering of the body o Ex. Skin or lining of intestines o Sarcomas – originate from tissues that support the body o Ex. Bone or muscle o Leukemias – originate from the bone marrow and spleen o Lymphomas – originate from lymph nodes Tumor Treatment o Surgery – cut out cells and surrounding tissue if possible o Radiation – high energy radiation o Damages DNA of rapidly dividing cells Side-effects: sterility (harms ovaries and testes) o Chemotherapy – Drugs that disrupt specific steps in the cell cycle o Paclitaxel (Taxol) – “freezes” mitotic spindle fibers o Vinblastin – prevents spindle fiber formation Side-effects: hair loss, digestive issues, lowers immune system o Endostatin – prevents the recruitment of new blood vessels (angiogenesis)