Cell-to-cell Adhesions Notes

313 tonicity and osmotic water movement hypotonic

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Unformatted text preview: ide 1 • osmosis ceases; dynamic equilibrium exists Assisted membrane transport o Carrier ­mediated transport o Facilitated transport o Active transport o Vesicular transport Tonicity of extracellular solution o Determines whether cell remains same size, swells, or shrinks when a solution surrounds the cell  Isotonic solution (cell remain the same size)  Hypotonic solution (cell swell)  Hypertonic solution (cell shrinks) Fig. 3.13 – tonicity and osmotic water movement Hypotonic solution  Solution of low concentration than another solution  4 mM sucrose solution is hypotonic to a 40 mM sucrose solution  sucrose is a big bulky molecule and CANNOT cross the cell membrane  net movement of water would be INTO the cell.  Cell will swell with water  Mass of the cell increases  Water moves in both directions but the majority of water will move inside the cells Isotonic solution  Solution of equal osmotic pressure  Normal healthy conditions  40 mM sucrose solution is isotonic to a 40 mM sucrose solution  net movement of water would be equal  cell wont gain or lose water.  The mass of the cell wont change Hypertonic solution  Solution of higher osmotic pressure than another solution  40 mM sucrose solution is hypertonic to a 4 mM sucrose solution  net movement of water would be OUT of the cell  the cell will shrink from the lost water  the mass of the cell will decrease  o o o Kinds of Membrane Transports • Assisted membrane transport o Carrier ­mediated transport  Accomplished by membrane carrier undergoing a conformational change  Can be active or passive, depending on the concentration gradients  Characteristics that determine the kind and amount of material that can be transferred across the membrane  Specificity  Saturation  Competition o Types of assisted membrane  Facilitated diffusion (passive transport)  Substances move from a higher concentration to a lower concentration  Requires carrier molecule (carrier ­mediated transport)  Example: glucose transport into cells  Fig. 3.14 – model for facilitated diffusion, a passive form of carrier ­mediated transport...
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