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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