Membrane transport mOsm(milliosmolar)or mOsm/ =an index of the concentration of particles per liter of solu mM(millimolar)or mML an index of the concentration of molecules dissolved per liter of solution isotonic solutions 300 mOsm= 150 mM NaCl (one NaCl molecule yields two particles 300 mOsm= 300 mM glucose The 300 mOsm is rounded off from the true value of 285 to 290 mOsm PROTEIN (CARRIER)-MEDIATED TRANSPORT Protein carriers transport substances that cannot readily diffuse across a membrane. There are no transporters for gases and other lipid-soluble substances because these substances read penetrate cell membranes. Characteristics Common to All Protein-Mediated Transport Rate of transport: A substance is transported more rapidly than it would be by diffusion, because the membrane is not usually permeable to any substance for which there is a transport protein Saturation kinetics: As the concentration of the substance initially increases on one side of the embrane, the transport rate will increase. Once the transporters become saturated, transport rate is maxima (TM=transport maximum). TM is the transport rate when the carriers are sat- urated. It is directly proportional to the number of functioning transporters Chemical specificity: To be transported, the substance must have a certain chemical structure Generally, only the natural isomer will be transported (e.g., D-glucose but not L-glucose Competition for carrier: Substances of similar chermical structure may compete for the same trans porter. For example, glucose and galactose will generally compete for the same transport protein types of Protein Transport acilitated Transport( Passive Process Net movement is always down a concentration gradient. It is the concentration gradient that drives both facilitated transport and simple diffusion Active Transport(Active Process Net movement is against a concentration gradient Requires chemical energy (ATP) medical 5..... MembraneTransport mOsm (milliosmolar) or mOsmIL =an index of the concentration of particles per liter of solu￾tion. mM (millimolar) or mM/L =an index of the concentration of molecules dissolved per liter of solution. isotonic solutions =300 mOsm = 150 mM NaCl (one NaCl molecule yields two particles in solution). 300 mOsm =300 mM glucose The 300 mOsm is rounded off from the true value of 285 to 290 mOsm. PROTEIN(CARRIER)-MEDIATEDTRANSPORT Protein carriers transport substances that cannot readily diffuse across a membrane. There are no transporters for gases and other lipid-soluble substances because these substances readily penetrate cell membranes. CharacteristicsCommonto All Protein-MediatedTransport Rate of transport: A substance is transported more rapidly than it would be by diffusion, because the membrane is not usually permeable to any substance for which there is a transport protein. Saturation kinetics: As the concentration of the substance initially increases on one side of the membrane, the transport rate will increase. Once the transporters become saturated, transport rate is maximal (TM =transport maximum). TM is the transport rate when the carriers are sat￾urated. It is directly proportional to the number of functioning transporters. Chemical specificity: To be transported, the substance must have a certain chemical structure. Generally, only the natural isomer will be transported. (e.g., D-glucose but not L-glucose). Competition for carrier: Substances of similar chemical structure may compete for the same trans￾porter. For example, glucose and galactose will generally compete for the same transport protein. Typesof ProteinTransport FacilitatedTransport(PassiveProcess) Net movement is always down a concentration gradient. It is the concentration gradient that drives both facilitated transport and simple diffusion. ActiveTransport(ActiveProcess) Net movement is against a concentration gradient Requires chemical energy (ATP) iiieilical 5