BIOL 1202 Lecture Notes - Lecture 12: Membrane Transport Protein, Electrochemical Gradient, Lipid Bilayer
Document Summary
Lipid bilayers in cells are selectively permeable. Cells are impermeable to ions, allowing large differences in intracellular (ic) vs extracellular (ec) fluid ion concentrations. Na+ most abundant cation in ecf, k+ most abundant in icf charges need to be. There is a slight imbalance concentrated near the plasma membrane (slightly negative electrically balanced by anions. Negative voltage inside cell relative to outside. Osmosis - water diffuses from area of low solute to high solute concentration. Na+ electric gradient: wants to move inside cell from pos+ to neg- charged area; Na+ chemical gradient: wants to move inside cell from high to low concentration. Charged molecules have both a charge gradient (electric) and concentration gradient (chemical) that affect their ability to move across membranes. Most plasma membranes have a charge (voltage) difference across them. Inside is usually negative relative to outside. This favors entry of cations and opposes entry of anions. Uncharged molecules move based on concentration gradient alone.
