Biology 1020 lecture 10 Membrane structure and function 2

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  1. Tonicity
    Total solute concentration
  2. Isotonic
    Solutions equal total solute concentration
  3. Hypertonic
    Higher total solute concentration
  4. Hypotonic l
    Lower total solute concentration
  5. Osmosis some terms
    Water diffuses from a hypotonic solution (total solute) to a hypertonic solution (total solute)

    Each solutes diffuses down its own concentration gradient. High to low
  6. Osmosis
    Some water molecules can move through the membrane in spaces created by the lateral movement of lipids
  7. Osmosis in cells lacking cell walls
    Cell in Hypotonic solution: the cell becomes lysed

    Cell in Isotonic solution: the cell is normal

    Cell in Hypertonic solution: the cell becomes shriveled
  8. Osmosis in cells with cell walls
    • -In Hypotonic solution: The cell is turgid (normal and happy)
    • -In Isotonic solution: The cell is flaccid (limp)
    • -In Hypertonic solution: The cell is plasmolyzed

    Plants rely on the influx of water to stay turgid (stiff)

    Plasmolysis cell loses water, shrivels pulls away from the cell wall
  9. Osmoregulation
    Paramecium lives in hypotonic pond water

    Water diffuses in, collected in contractile vacuoles, is pumped out
  10. Membrane transport
    • Passive transport: (with concentration gradient)
    • - Diffusion
    • - Facillated

    Active Transport (against concentration gradient)
  11. Facilitated diffusion
    Transport proteins: Speed the passive movement of molecules across the plasma membrane

    Corridors for specific molecules or ions

    Channel and carrier proteins
  12. Faciliated diffusion: Channel proteins
    Provide corridors that allow a specific molecule or ion to cross the membrne
  13. Faciliated diffusion: Carrier Proteins
    • Undergo change in shape
    • Translocates the solute-binding site across the membrane
  14. Faciliated diffusion: channel proteins
    Aquaporins: for faciliated diffusion of water

    ION channels: open or close in response to a stimulus (gated channels)
  15. Aquaporins
    • Channel proteins for water
    • Discovered in 1922
    • - Previously thought that water only crossed membranes passively (did not explain rapid movement)

    • They are tissue specific
    • Very important in water uptake by plants

    • Aquaporin function implicated in:
    • - Congenital cataracts
    • - Congestive heart failure
    • - Diabetes insipidus
    • - Brain edema
  16. Diabetes insipidus and aquaporins
    Aquaporins allow water to be move from kidney tubules to blood (concentrates urine)

    • A mutation/defect in aquaporin production causes:
    • - Water not reabsorbed
    • - Urine not concentrated
    • - Excessive urination
    • - Extreme thirst
    • - Dehydration
  17. Active Transport
    • Transport against a concentration gradient
    • Allows cells to maintain concentration of solutes different from their surroundings
    • Specific membrane proteins

    • Requires energy
    • ATP transfers a phosphate group to the transport protein
    • Protein changes shape
    • Translocates a solute across the membrane
  18. Phosphate: ATP
    ATP reacts with water (hydrolysis) ---> P + ADP + energy
  19. Active transport: Sodium - potassium pump
    • 1. Cytoplasmic Na+ binds to the sodium-potassium pump
    • 2. Na+ binding stimulates phosphorylation by ATP (a phosphate is then attached to the protein and ADP and energy is released)
    • 3. Phosphorylation causes the protein to change its shape. Na+ is expelled to the outside
    • 4. K+ binds on the extracelluslar side and triggers release of the phosphate group
    • 5. Loss of the phosphate restores the protein's original shape
    • 6. K+ is released, and the cycle repeats
  20. Active transport: Membrane potential (electricity)
    • Voltage difference across a membrane (-50 to -200mV)
    • created by differences in the distribution of positive and negative ions

    • Na-K pump
    • 3 Na+ outside
    • 2 K+ inside
    • Therefore, outside of cell tends to be more positively charged.
  21. Electrochemical gradient
    • Electro - charges of ions
    • Chemical - concentration of ions
  22. Electrogenic pump
    Transport protein that generates voltage across a membrane

    • Major electrogenic pumps
    • Animal cells: Na-K pump

    Plants, Fungi, bacteria cells: proton (H+) pump
  23. Proton pump
    Pumps protons into the extracellular fluid
  24. Active transport: co-transport
    Active transport of a solute (proton pump) indirectly drives transport of another solute

    • ex. Hydrogen ions generated by proton pumps to drive active transport of nutrients into plant cells.
    • - Proton pumps increases the concentration of H+ outside the cell (potential energy)
    • - H+ coupled with sucrose
    • - Sucrose hydrogen co-transport uses diffusion of H+ down the gradient to drive uptake of sucrose
    • ATP indirectly providing energy through proton pump
  25. Bulk membrane transport
    • Large molecules, such as polysaccharides and proteins, cross the membrane in bulk via vesicles
    • Requires energy
    • Types of bulk transport
  26. Bulk membrane transport: Exocytosis
    Transport vesicles migrate to the membrane, fuse with it, and release their contents

    Secretory cells use exocytosis to export their products (e.g. insulin)
  27. Bulk membrane transport: Endocytosis
    Extension of cytoplasm-pseudopodia-surround material
  28. Endocytosis - pinocytosis
    "Cell-sipping"- infolding of plasma membrane . Sometimes receptor mediated
  29. Bulk membrane transport: Receptor mediated endocytosis (specific)
    • The receptor matches the ligand
    • A coated (coat protein) pit and a coated besicle formed during receptor-mediated endocytosis (TEMS)
  30. What is metabolism?
    • All of the chemical reactions in an organism
    • Emergent property
    • Cells extracts energy and apply energy to perform work.
    • Series of chemical reactions that build complex molecules or break down
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Biology 1020 lecture 10 Membrane structure and function 2
2013-10-05 18:59:58
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