BIOL 3755 Chapter Notes - Chapter 4: Fluid Compartments, Extracellular Fluid, Lipid Bilayer
Document Summary
Chapter 4 movement of solutes and water across cell membranes. Diffusion rate versus distance in air than in water: diffusion provides movement over short distances between blood, interstitial fluid, and intracellular fluid. Ions such as sodium, potassium, chlorine, calcium diffuse across plasma membranes at much faster rates than would be predicted from their very low solubility in membrane lipids. Ion channels ~ small passages in plasma membrane formed by integral membrane proteins and through which certain small diameter molecules and ions can diffuse: can show selectivity for type of ion or ions that can diffuse through them. Based on channel diameter, charged and polar surfaces of polypeptide subunits that form channel walls and electrically attract or repel ions, and number of water molecules associated with ions. Facilitated diffusion: facilitated diffusion ~ system using transporter to move molecules from high to low concentration across membrane; energy not required.
