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Unformatted text preview: Cell Membrane Structure Membrane phospholipids are AMPHIPATHIC polar (hydrophilic) and nonpolar (hydrophobic) regions Polar regions of amphipathic molecules form hydrogen bonds with water. When mixed with water, phospholipids spontaneously assemble to form Micelles or Bilayers Cholesterol = steroid lipid; important in membrane structural and mechanical stability Peripheral Proteins Attach to either inner or outer face of membrane Integral Proteins Protrude partly or all the way across membrane Include channel proteins and carrier proteins Cell Membrane Function Cell membrane has property of selective permeability Cell obtains nutrients and removes wastes via cell membrane transport mechanisms * Simple and Carrier-Mediated (Facilitated) Diffusion * Active mechanisms require ATP Active transport (primary and secondary); endocytosis, exocytosis Physics of Simple Diffusion (Passive) First, look at diffusion in general (then look at cells) Diffusion = movement of molecules as a result of random thermal motion Simple Diffusion between Compartments (Passive) Terms to understand: FLUX - movement of solute in a direction NET flux - the net of flux (diffusion) Equilibrium - when net flux = 0 Net flux is from HIGH to LOW concentration What factors affect the magnitude of net flux? Magnitude of concentration gradient Temperature- increase temperature = increase flux Mass of molecule Surface area for diffusion 1- increase surface area = increase flux Medium through which molecules are moving Driving force? The driving force behind diffusion is the difference in concentration gradient Diffusion Rate vs. Distance Diffusion times increase in proportion to the distance squared * 10 micrometers vs. 10 centimeters * Few seconds vs. 11 years Thickness of the cell membrane? < .01 micron Diffusion is only favored over a short distance Diffusion across a boundary When considering diffusion between compartments, must also take into account the permeability of the boundary in addition to the other factors affecting rate + magnitude of diffusion The cell membrane...
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This note was uploaded on 03/19/2012 for the course BIO 2000 taught by Professor Ewr during the Spring '12 term at Alabama.
- Spring '12