Authentic Biochemistry

•Free energy change(chemical potential difference) for transporting 1 mole of a substance from region where its concentration is C1 (e.g., Cout) to region where its concentration is C2 (e.g., Cin): ∆G= RTln(C2/C1) (favorable with ∆G< 0 if C2< C1) •Transport of ionsacross membrane (must consider electrical potential in addition to concentration difference): ∆G= RTln(C2/C1) + ZF ∆Y (Z=charge of ion, F=Faraday’s constant, ∆Y=membrane  electrical potential in volts) •Coupled transport (active transport): ∆G= RTln(C2/C1) + ∆G´ (∆G´ of coupled process, such as ATP hydrolysis, may be  negative enough to compensate for unfavorable transport  against concentration gradient when RT ln (C2/C1) > 0) •Diffusional transport: movement of substance from high to low concentration across membrane (down concentration gradient) –Non-facilitated diffusion across lipid bilayer (slow for most biological substances) –Facilitated diffusion (accelerated diffusion by making membrane more permeable to specific tr