AN SC 310 - 3

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AN SC 310 - 3
2012-09-19 23:48:49
AN SC 310

Lecture 3 - Movement of Substances Across Membranes
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  1. Describe the 2 different types of transport
    Passive - spontaneous, moves down concentration gradient, no energy required

    Active - not spontaneous, moves up concetration gradient, energy required, involves a pump
  2. Define Driving Forces
    Forces which act to move particles
  3. What are the 3 different types of driving forces?
    • Chemical
    • Electrical
    • Electrochemical
  4. Describe chemical driving force
    • Concentration gradient
    • "Pushes" particles from high to low concentration
  5. What is the direction of chemical driving force?
    • Down the chemical gradient
    • High to Low concentration
  6. Describe electrical driving force
    • Membrance potential (Vm)
    • Due to the unequal distribution of anions and cations across the cell membrane
    • Charge seperation = source of energy
  7. What does the direction and magnitude of electrical driving force depend on?
    • Polarity of cell
    • Charge on particle
    • Strength of Vm
  8. Describe Electrochemical Driving Force
    • Total force acting on particles
    • Direction is the sum of chemical and electrical forces
    • Magnitude = larger force +/- smaller force
  9. What is Equilibrium Potential (Ek/Ex)?
    • Where force = 0
    • No movement of particles in/out of cell
  10. If Vm > Ek, what is the dominant force?
    Electrical, therefore electrochemical would move in the direction of the electrical driving force
  11. What are the 3 types of passive transport?
    • Simple diffusion
    • Facilitated diffusion
    • Diffusion through channels
  12. Define simple diffusion
    Passive transport through the bilipid layer without need of a carrier or channel
  13. What factors affect the rate of simple diffusion?
    • Magnitude of the driving force
    • Membrance surface area
    • Membrane permeability
  14. What factors affect membrane permeability?
    • Lipid solubility of diffusing particles
    • Size and shape of diffusing particles
    • Temperature
    • Thickness of membrane
  15. Define facilitated diffusion
    Passive transport through a carrier
  16. What are the characteristics of a carrier?
    • Transmembrane protein
    • Has binding sites for specific particles
    • Binding occures one side at a time (internal/external)
    • Random conformation changes
  17. What factors affect the rate of facilitated diffusion?
    • Rate of transport of each carrier
    • # of carriers in membrane
    • Concentration gradient
  18. Define diffusion through channels
    Passive transport through a channel
  19. What are the characteristics of a channel?
    • Transmembrane protein
    • Functions like a pore
    • Substance specific
  20. What are the 2 types of channels?
    • Aquaporins - water channels
    • Ion channels - leak channels, gated channels
  21. What factors affect the rate of transport of diffusion through ion channels?
    • Transport rate of each channel
    • # of channels in membrane
  22. What are the characteristics of a pump?
    • Type of membrane protein
    • Function as transporter & enzyme
    • Can harness energy
    • Have specific binding sites
    • Demonstrate saturation
  23. What are the 2 types of active tranport?
    • Primary active transport
    • Secondary active transport
  24. Where is the energy for primary active transport obtained?
    • High energy compound
    • Usually from ATP hydrolysis
  25. Give an example of primary active transport
    Na+/K+ pump

    Na+ from ICF binds to receptor, P binds to receptor, receptor changes conformation, Na+ released into ECF, K+ from ECF binds to receptor, P removed, receptor changes conformation, K+ released into ICF
  26. Where is the energy for secondary active transport obtained?
    • Released from ion diffusion
    • Results from previous active transport of ion

    Particles hitch a ride on the pump as an ion diffuses. Can be in same direction (Na+/Glucose pump) or opposite (Na+/H+ pump)