PSL300H1 Lecture Notes - Membrane Transport Protein, Active Transport, Aquaporin
Document Summary
Non-polar end is 2 long fatty acid chains (hydrophobic); Essential for efficient carrier and channel protein function. Cholesterol stabilizes membrane; prevents diffusion of polar molecules across it. Matrix of long carbohydrate filaments; fill extracellular space, slowing diffusion. If a substance can cross the membrane by any means, the membrane is permeable to that substance. Polar molecules and ions need the help of proteins - channels or carriers - to cross. 4-5 protein subunits fir together such that a central pore is created through membrane. "pore loops" of the protein molecules dangle inside the channel. Physical properties of the pore loops create a selectivity filter: only specific molecules can diffuse through. Family of channels specific for water and small non-ionic molecules (glycerol, urea) Narrow part with diameter about the size of a water molecule (~4 a) ; diffusion 3-5 fold slower than bulk water diffusion. Membrane channels generally are not kept perpetually open.
