Plasma membrane Fluidity Mosaic • Hydrophobic interactions (weak) • Lateral movements of PL (not fixed) • Asymmetrical protein embedding • Many functions of proteins tors Affecting Fluidity Of Membrane Temperature temp kinetic energy lateral motion fluidity • Low temp – gel phase (phase transition) • High temp – fluid phase Length of FA length hydrophobic interX n heat energy melt g pt • > Solid / gel like at room temperature Degree of FA saturation saturation kinks packing fluidity Amt of cholesterol mol (intracellular membranes= rare) stability • Chol intercalated/wedged in PM, enhancing mechanical stability • Regulates Fluidity (Dual effects on the fluidity – temp buffer) • High temp = interfere w PL’s motions, so fluidity • Low temp = packing of PL = fluidity • Affects permeability 11 permeability by filling in spaces, so plugging transient gaps 2) Prevent small polar mol & ions from going thru *** Transport across Membranes *** cell = s + p The net movement of freely moving water mol from a region of LESS NEGATIVE water potential to a region of MORE NEGATIVE water potential through a 0 - 20 - 40 Water potential [solute] Hypotonic Isotonic Hypertonic Less Neg Equal More Neg - H 2 0 > - - H 2 0 enters - lysis - H 2 0 = - No net change in cell volume - H 2 0 < - - H 2 0 leaves - - H 2 0 > - - H 2 0 enters - Turgid - H 2 0 = - No net change in cell volume - H 2 0 < - - H 2 0 leaves - Flaccid / plasmolysed Cell Wall Maintains shape 10nm amphipathi c hydrophill ic hydrophobi c Intrinsic/Integral • largely hydrophobic • Deeply embedded • Weak hydropho interX n • protein can move (fluidity) • Detergents & solvents Peripheral • hydrophillic • loosely bound • cytoskele of cell • ECM’s fibres • pH / ionic changes Stabilize PM & shape anchorage recogniti on enzymatic receptor joining Cell identit y 3 f(x) sequent ial Chem signalscommunicati on 1 protein may more than 1 function p = pressure the wall is exerting on the cell’s content, pushes water out, so its (+) s : affected by [solute]