Plasma membrane FluidityMosaic Hydrophobic interactions (weak) Lateral movements of PL (not fixed) Asymmetrical protein embedding Many functions of proteins Factors Affecting Fluidity Of Membrane 1)Temperature  temp   kinetic energy   lateral motion   fluidity Low temp – gel phase (phase transition) High temp – fluid phase 2)Length of FA  length   hydrophobic interX n   heat energy   melt g pt > Solid / gel like at room temperature 3)Degree of FA saturation  saturation   kinks   packing   fluidity 4)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  permeability by filling in spaces, so plugging transient gaps 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 selectively permeable membrane Water potential  [solute] HypotonicIsotonicHypertonic 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 - shrivelled - 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 amphipathic hydrophillichydrophobic 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 anchoragerecognitionenzymaticreceptor joining Cell identity 3 f(x) sequentialChem signals communication 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]

Hydrophobic O 2, CO 2 N 2 Benzene, H 2 O Small Uncharged Polar Urea, glycerol, H 2 O Charged Polar H + Na + HCO 3 - K + CA 2+ Cl - Mg 2 + Large Uncharged Polar Glucose, Sucrose - Concentration gradient  concentration =  rate - DISTANCE over wh diffusion occurs ↓ distance =  rate - AREA across wh diffusion occurs  area =  rate - STRUCTURE through wh diffusion occurs  # of pores/ channels / carriers =  rate - SIZE and TYPE of diffusing molecule ↓ size =  rate - Temperature  Temperature =  KE =  rate Factors affecting diffusion rate Bulk transport Facilitated diffusion Diffusion/ osmosis Active Gated Channel Passive Uniport Symport Antiport Specific binding sites Transport Proteins Help polar mol cross hydrophobic PM mol move down or against conc grad specificity makes PM specific in transport jobs Active Transport Ingestion of bact by wbcMucus secretionCa 2 + secretion KIV nervous system ‘nursing’ of human egg cells Cholesterol uptake KIV cell signaling & homeostasis Na +/ K + pump Proton Pump Glu pump Conformation change

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