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United States (323,972)
Life Science (261)
LIFE 210 (38)

Passive transport, diffusion, active transport, glucose transport

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Life Science
LIFE 210
Paul Laybourn

21 September Introduction – some definitions Lipid bilayers/monolayers are permeability barriers Molecules can cross by simple, passive diffusion Molecules can cross through channel and carrier proteins Transport can be passive or active Passive – drive by diffusion, -ΔG, with concentration or charge gradient (down hill) Active - +ΔG, against concentration or charge gradient (up hill) Primary active – uses energy source directly Secondary active – uses energy source indirectly ΔG of Concentration Gradients Across Membranes ΔG‡ lowest for nonpolar S; highest for charged S ΔG mostly due to +ΔS [S ¿ ΔG = RT ln [SOUT ] [S ¿ If [SOUT > [SIN then [SOUT ] < 1 S S Ln [¿¿OUT ] < 0 [¿¿¿] ¿ ¿ So ΔG < 0 Simple Diffusion – Passive Hydrophobic molecules – free diffusion Small uncharged polar molecules – slow diffusion Large uncharged polar molecules – very slow diffusion Ions – no diffusion Small uncharged polar molecules, large uncharged polar molecules, and ions all require transporters Passive Facilitated Diffusion and Transport Movement with concentration or charge gradient (down hill) – electrochemical gradient Pores or channels – amphipathic α-helices, β-barrels Some are gated – open and close in response to signal Carrier Proteins Proteins bind molecules Go through conformation change Catalyzed reaction, enzyme kinetics Active Transport Movement against concentration or charge gradient (up hill) – electrochemical gradient Primary Active Transport Uses energy source directly Energy sources: ATP, NADH, light Example: Na
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