Chapter 4 Cell Membrane Transport How Do Cells Transport Nutrients and Materials into the Cell 1 molecule of glucose yields 38 molecules ATP Cells also metabolize other monosaccharides such as fructose galactose and mannose As electrons pass through these carriers they uElize the released energy to move hydrogen ions against their gradient to create a store of potenEal energy Metabolism of Carbohydrates Metabolism of Fats Metabolism of Proteins How Do Cells Acquire the Materials They Need Mechanisms of Membrane Transport Driving Forces AcEng on Molecules Chemical Electrical Facilitated Di usion of Glucose Facilitated Di usion of Glucose Glucose binds GLUT 1 on the exterior of the membrane and this binding causes a conforma5onal change in the protein which transports glucose into the interior of the cell Is Facilitated Di usion Always Enough Na K Pump Most cells contain transport proteins which harness the energy from ATP acEve transport to pump ions against their concentra5on gradient The sodium potassium pump transports Na and K ions in opposite direcEons across the plasma membrane 3 Na ions out for every two K ions in Na K Pump Na Glucose Symporter Na Linked Symporters Import Glucose and Amino Acids into Cells Against Their ConcentraEon Gradients Epithelial Solute Transport The Na electrochemical gradient established by a Na K pump provides the energy to drive the ac5ve transport of glucose against its concentraEon gradient across the apical membrane Glucose then passively exits the cell moving down its concentraEon gradient via a carrier protein in the basolateral membrane Na Glucose Symporter Transcytosis During transcytosis a large molecule is taken into the cell by endocytosis The vesicle then travels to the opposite side of the cell and fuses with the plasma membrane to release its contents by exocytosis CysEc Fibrosis CysEc brosis is caused by a defect in a type of chloride channel found in the apical membranes of epithelial cells that line the respiratory tract The defect impedes Cl transport which indirectly interferes with transport of Na and there is no gradient to drive water secre5on