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Intercellular Communication II

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Christopher Perumalla

Intercellular Communication II Cell Membrane Transport continuedWe already know that very small lipid soluble molecules such as oxygen can easily pass through the membrane whereas very large polar molecules or proteins cannot get through easily without certain mechanisms Passive transport is spontaneous moving down the concentration gradient and does not require cell energyThe types of passive transport are simple diffusion facilitated diffusion and diffusion through channels What are the mechanisms involved in crossing the membrane For simple diffusion no membrane proteins are needed and the transport is through the bilipid layer Simple diffusion functions well for small lipid solublesThey can pass either directly through the phospholipid bilayer or can pass through poresThis is a great tool for communication and exchange of materials for short distances If there is a concentration gradient if one side is more concentrated than the other the molecules move in a random movement across the bilayer or through poresThere are three factors that affect simple diffusion the magnitude of the driving force the membrane surface area and the membrane permeability In simple diffusion the rate of transport is directly proportionate to the concentration gradient The net flux depends on the magnitude of the concentration gradient the greater the concentration gradient the greater the fluxAlso the rate of diffusion depends on the permeability of the substanceA membrane with high permeability will result in higher net flux when compared to a membrane with low permeability If a membrane is open to certain ions there will be an increase in the flux
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