Pores and Transport Channels

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medstudent2017
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312125
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Pores and Transport Channels
Updated:
2015-11-26 08:04:09
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channels pore
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Pores and Transport Channels
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  1. What Non-polar lipid soluble substances can pass the cell membrane without assistance
    • Lipid-based hormones (aldosterone),
    • O2,
    • CO2,
  2. What are the three types of membrane transport
    • Diffusion (passive)
    • Carrier-mediated Transport
    • Vesicular Transport
  3. Two types of Diffusion
    • Diffusion through plasma membrane (simple diffusion)
    • Diffusion through channels/pores
  4. Types of Carrier-mediated Transport
    • Facilitated diffusion (Passive)
    • Active Transport
    • - Primary active transport
    • - Secondary active transport
  5. Passive transport is defined as
    Transporting molecules from a region of high concentration to a region of low concentraction.
  6. Membrane Permeable Molecules
    • O2
    • H2O (to an extent)
    • CO2
    • steroid hormones
    • thyroid hormone
  7. What are some examples of Pores
    • Porins
    • Connexins
    • Aquaporins
  8. Traits of pores are
    • Always open on both sides (no gate)
    • Substances move through a pore “downhill” or down the concentration gradient
    • Subunits undergo no conformational changes
    • Do not exhibit saturation
  9. Fick’s Law of Diffusion
    Jx = PxA (C1-C2)

    • Jx (Rate of Transport)
    • A (Surface area)
    • w (Membrane thickness)
    • C1 (area of High conc.)
    • C2 (area of Low conc.)
  10. What are the charecteristics of Channels
    • 1. Not always open
    • 2. Contain a gate
    • 3. Gate must receive a signal to open (stretch, Δ voltage, ligand binding)
    • 4. “Downhill” movement
    • 5. Do not exhibit saturation
    • 6. Most are selective for the molecules they transport
  11. Aquaporin are pores found in
    The Kidneys
  12. The opening/closing (gating) of ion channels can be regulated by:
    • Change in voltage
    • Binding of a chemical messenger (ligand)
    • Mechanical forces (stretch)
  13. Carrier mediated transport has what qualities
    • Specificity
    • Saturation limited
    • Competition (different substances that can be carried by the same transport compete slowing it down)
  14. Transporter Characteristics
    • 1. Not always open
    • 2. Transported molecules bind to the carrier & subunits undergo a conformational change
    • 3. Responsible for facilitated diffusion; move substances “downhill” without ATP
    • 4. Responsible for secondary active transport; moves substances “downhill” and/or “uphill”
    • 5. Transporters can be saturated.
  15. Active Transport
    • Transport against a gradient
    • Requires energy (directly or indirectly)
  16. Primary Active Transport
    • 1. Solutes are transported against their concentration gradient.
    • 2. Energy required to transport molecules “uphill” is derived from the breakdown of ATP or GTP.
  17. Pumps charecteristics are
    • 1. Not always open
    • 2. Solute binds to pump, then pump undergoes a conformational change; No true “gate”
    • 3. Responsible for primary active transport, requires ATP to move a substance “uphill”.
    • 4. Pumps can be saturated
    • 5. Highly selective for the molecule they transport
  18. What is the most common type of pump in the cell
    • Sodium Potassium ATPase
    • 3 Sodium from inside of cell to the outside
    • 2 Potassium from the outside in
    • *Requires one ATP molecule
    • In cardiac and smooth muscles
  19. Secondary Active Transport
    • Does not use ATP directly but instead takes advantage of a previously established concentration gradient
    • Na/Ca transport (3Na in 2Ca out) uses gradient of high Na outside the cell built by Na/K+ ATPase
  20. Cotransport (Symporter)
    Energy from one gradient drives transport of another molecule against its gradient
  21. Countertransport (Antiporter)
    • e.g. as Na+ moves
    • into the cell, molecule X is pumped out.
  22. Give an Example of a Secondary Active Transport
    • Sodium Glucose transporter in kidney
    • or
    • Sodium-Calcium exchanger in cardiac muscle

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