Second Half Lecture 3

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26 Mar 2012
Lecture 3 Mar. 8/12
Membrane Transport of Small Molecules
Lipid bilayer permeability
Hydrophobic (non-polar) molecules are permeable
Polar molecules and ions are impermeable (H2O exception)
Movement across membrane is through diffusion, high to low concentration
Membrane transport proteins overview
Used to transport polar molecules and ions across membrane
Multi-pass molecules
Ex. alpha-helices/beta barrels
Transporter proteins
Carrier proteins
Binds to specific solute, undergoes conformational change
Conformational change allows protein to physically direct solute movement
Can be either passive or active transport
Channel proteins
Create a passage to allow the passing of molecules
Passive transport
Electrochemical gradient (EG)
Determines molecular transport ability
Depends on concentration of molecules + ion charges around membranes
High to low concentration favoured
Attraction of opposite charge on opposite end of membrane is favoured
Motive force: measurement of feasibility for molecules (based on charge) to cross
membrane, charges include –ve, +ve and neutral
Types of transport
Passive: Diffusion across membrane from high to low concentration, with
electrochemical gradient, no energy needed
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