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Intercellular Communication I

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University of Toronto St. George
Christopher Perumalla

Intercellular Communication I1Factors affecting the direction of transport 2 Rate of transport 3 Passive transport 4Active transport 5Osmosis passive transport of water across membranes 6Transport of material within membrane bound compartments 7Epithelial transport movement of molecules across two membranesMembranes act as a barrier to separate the ICF from the ECF and restricts the passage of movement of materialThe membrane also allows some materials to get through such as oxygen carbondioxide glucose etc How do we restrict the entry of some material yet let some others inThe membrane is selectively permeable allowing some things to go through but not othersThe definition of membrane permeability is that if a substance can cross a membrane by any means the membrane is set to be permeable to that substanceIn order to live cells must be able to execute exchanges with its environment For example since all cells require oxygen and need to get rid of carbondioxide small molecules must be able to move across the membrane to transport things from and to the cell The transport across the membrane is an absolute requirement in lifeWhich molecules are able to cross the membrane Non polar molecules and small molecules such as oxygen water and fatty acids are easily transported across the membrane However polar molecules large molecules and proteins such as glucose and sodium are normally not transportedThe polar molecules cannot get through since the membrane is composed of a phospholipids bi layerIn short membrane selectivity depends on molecule size liposolubility and ion chargeHow can we move things across the membraneWhat are the ways in which these molecules are transported The transport across the membrane can be divided into two categories passive transport and active transportPassive transport is spontaneous and moves down or with the concentration gradientActive transport is not spontaneous and moves against the
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