BIO 212 Exam 4

• Structure of bacterial flagella

  • Complex structure
  • Assembled from many different proteins
  • Have a molecular motor powered by a proton gradient (not ATP)
• Amoeba movement using pseudopodia


  1. ATP powers interactions between actin and myosin in the cytoskeleton

  3. Plasma membrane is pushed out in a specific direction, forming pseudopodia

  2. The cytoplasm streams along behind
• Protist movement using cilia


  • Requires ATP
  • Microtubules, made of the protein tubulin, move the cilia to produce movement
• Protist movement using flagella


  • Requires ATP
  • Microtubules, made of the protein tubulin, move the flagella to produce movement
• Most fungi are NOT capable of movement
• Fungi colonize their environment using spores spread by wind, water, or other organisms
• Tropism


  A growth or turning movement in plants, in response to an environmental stimulus
• Phototropism


  The directed movement of plants in response to light
• Plants bend toward blue light
• Phototropins


  Plant photoreceptors that detect blue light and initiate phototropic responses
• Plant response to blue light

  1. Chloroplasts move within leaf cells to positions that optimize light absorption

  2. Stomata open to allow carbon dioxide to diffuse into cells as blue light triggers photosynthesis

  3. The stem elongates
• Auxin


  A hormone produced at the young shoot tip (called coleoptile), which is broken down by the sun on the bright side, promoting cell elongation on the shaded side to cause the coleoptile to bend towards the light
• Acid Growth Hypothesis


  Loosening of the cell wall via acidification/expansins (specialized proteins) coupled with high turgor pressure results in cell elongation
• Cell elongation mechanism


  1. Protons are pumped from the cell to the cell wall by ATP-driven pumps

  2. Expansin is made in the cell and exported to the cell wall

  3. Proton pumping generates a membrane potential: the inside of the membrane becomes more negative; potassium ions flow in to compensate

  4. As the concentration of potassium in the cell increases, water follows (osmosis) and the turgor of the cell increases
• Gravitropism


  The ability of plants to move or grow in response to gravity
• Gravity sensing in plants


  • Occurs in specialized cells with amyloplasts located at the center of the root cap
  • Amyloplasts are dense, starch-storing organelles that respond to gravity by being pulled to the bottom of root cap cells
  • The position of the amyloplasts activates sensory proteins located in the plasma membrane, which initiate the gravitropic response
• Gravitropic response of roots


  1. Auxin inhibits elongation in roots

  2. When a root is placed horizontally, the amyloplasts activate sensor proteins which initiate responses that redistribute auxin, so there is more auxin on the bottom side of the root

  3. Cells at the bottom are inhibited, while cells at the top side keep elongating

  4. As a result the root bends
• Thigmomorphogenesis


  The growth response of plants to touch, producing short, stocky plants
• Thigmotropism


  Plant movement response (directional) to touch
• Thigmonastic movement


  Rapid, nondirectional movement of plants in response to touch, requiring a touch-receptor cell that transduces a mechanical signal to an electrical signal, i.e. to an action potential
• Action potentials in plant cells


  • Similar shape as in animal cells, but slower and involve different ions
  • The resting potential is maintained by ATP-driven proton pumps in the plasma membrane and potassium leak channels
  • The action potential is due to the movement of Ca2+ and Cl- ions
  • Move between cells via plasmodesmata
  • DO NOT form synapses
• Nutation


  The circular swaying movement of the tip of a growing shoot in plants, adaptive value by optimizing direction of growth toward supporting structures or light
• How does the bacterial flagellum create movement?

  Molecular motor from proton gradient drives clockwise (tumble) or counterclockwise (run) rotation.
• How do unicellular eukaryotes move?

  • Flagella - ATP powered microtubule movement
  • Cilia - ATP powered microtubule movement
  • Pseudopodia/cytoplasmic streaming - ATP powers actin and myosin contractions, push cytoplasm into pseudopodia, remaining cytoplasm streams behind
• How do action potentials cause movement in plants?

  When action potentials reach target cells, vacuoles fill or empty to create swelling or wilting of tissues
• Innate immune responses


  Responsible for the initial, quick, non-specific response to an attack by any pathogen
• Adaptive immune responses


  Responsible for a slower, highly specific response to a particular pathogen
• Innate immune system


  • Immediate, generic response against broad groups of pathogens
  • Carried out by white blood cells
  • Can broadly distinguish between groups of pathogens (e.g. bacteria vs fungi), but not specific strains within groups
• Components of the innate immune system

  • Physical barriers (e.g. skin)
  • White blood cells that can recognize and phagocytize pathogens
  • Protein-based chemical defense system called the complement
  • Inflammation process
• Pattern-Recognition Receptors


  Receptors that receive the molecular signal that a pathogen is present, e.g. toll-like receptors (TLRs)
• Inflammatory response


  1. Pathogen enters a wound

  2. Platelets release blood-clotting factors

  3. Injured tissue releases cytokines, which recruit immune system cells

  4. Mast cells secrete histamine, dilating blood vessels and making them more permeable

  5. Recruited neutrophils and macrophages remove pathogens by phagocytosis

  6. Chemical signals are released that stimulate tissue repair
• Antigen


  A foreign molecule that can elicit an immune response
• Antibody (immunoglobulin)


  A protein made by activated cells of the immune system that can bind a specific antigen
• Epitope


  The part of the antigen which is recognized by the antibody. A large antigen can have many epitopes. Each antibody recognizes only one epitope.
• Cytokine


  A chemical signal synthesized by cells of the immune system that acts locally on nearby cells (paracrine signaling)
• Major histocompatibility protein (MHC protein)


  A group of proteins that are found on the surface of all cells and are crucial to the recognition of the body's own cells and the immune response against pathogens
• Adaptive immunity


  • Specificity - antibodies and other components bind only to specific epitopes on specific antigens
  • Diversity - the immune system can recognize virtually any type of antigen
  • Memory - responses are stronger and quicker when an individual is exposed to antigens from previous infections
  • Self versus nonself recognition - molecules that are produced by an individual do not normally trigger an immune response
• Lymphocytes


  White blood cells that are the major cells involved in the adaptive immune response
• T lymphocytes (T cells)


  Mature in the thymus
• B lymphocytes (B cells)


  Mature in bone marrow