Topic 2

• Host cell


  The cell that uses the genetic material to replicate the virus particle
• Eukaryotic cell cycle


  1. Interphase

  2. Mitosis

  3. Cytokinesis
• Interphase


  The longest stage of the cell cycle, includes G1, S, and G2
• G1


  Cell increases in size, organelles double
• S phase


  DNA replication happens
• G2


  Further growth, preparation for mitosis, error check stage
• Nuclear division


  Mitosis or meiosis
• Cytokinesis


  Cytoplasm divides to create two new cells
• Mitosis


  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase
• Mitosis


  • Only one round of division
  • Genetically identical cells created
  • Diploid cells
  • Used for growth and repair
• Clonal expansion of B cells

  Example of growth through mitosis
• Prophase


  1. Chromosomes condense

  2. Centrioles move to opposite poles

  3. Spindle fibers form
• Metaphase


  1. Chromosomes line up along the equator

  2. Spindle fibers attach to centromeres and chromatids
• Anaphase


  Spindle fibers retract, pulling chromatids to opposite poles
• Telophase


  1. Chromosomes at poles become longer and thinner

  2. Spindle fibers disintegrate

  3. Nucleus reforms
• Mitotic index


  Percentage of cells in mitosis
• Binary fission


  1. Replication of circular DNA and plasmids

  2. Division of cytoplasm to produce two daughter cells
• Viruses are non-living, they inject their nucleic acid into the host cell which replicates the virus particles
• Fluid mosaic model


  Structure of cell and organelle membranes, composed of phospholipids, proteins, glycoproteins, and glycolipids
• Phospholipid bilayer


  Hydrophilic heads face outwards, hydrophobic tails face inwards
• Cholesterol


  Restricts lateral movement of other membrane molecules, makes membrane less fluid at high temperatures
• Membrane components


  • Peripheral/extrinsic proteins
  • Integral/intrinsic proteins
  • Glycoproteins
  • Glycolipids
• Peripheral/extrinsic proteins


  Provide mechanical support, connect to other proteins or lipids
• Integral/intrinsic proteins


  Protein carriers or channels involved in transport across the membrane
• Partially permeable membrane


  Only lipid-soluble and small molecules can pass by simple diffusion, other molecules require facilitated diffusion, active transport, or osmosis
• Simple diffusion


  Net movement of molecules from high to low concentration, no ATP required
• Facilitated diffusion


  Molecules diffuse through protein channels or carriers, still down concentration gradient
• Osmosis


  Movement of water from high to low water potential across a partially permeable membrane
• Isotonic, hypotonic, hypertonic


  Describe the relative water potential of a solution compared to a cell
• Active transport


  Movement of molecules from low to high concentration, requires energy (ATP) and carrier proteins
• Co-transport


  Active transport of one molecule (e.g. glucose) coupled to transport of another (e.g. sodium ions)
• Adaptations for rapid transport

  • Increased surface area (e.g. microvilli)
  • More transport proteins in membrane
• Self vs non-self


  Immune system can distinguish body's own cells from foreign/abnormal cells and pathogens
• Antigen


  Molecule that triggers an immune response, usually a protein on the surface of a cell
• Antigen variability


  Pathogens can mutate their antigens, reducing effectiveness of previous immunity
• Immune responses


  • Non-specific (phagocytosis)
  • Specific (cell-mediated by T cells, humoral by B cells)
• Phagocytosis


  Phagocytes (e.g. macrophages) engulf and destroy foreign particles or pathogens
• Cell-mediated immunity


  T cells respond to antigens presented on infected or abnormal body cells
• Antigen presenting cells display foreign or abnormal antigens on their surface to trigger T cell response
• Antigen presenting cells (APC)


  Any cell that presents a non-self antigen on their surface