O D Side-by-Side The thermodynamics of vesicle loading: Primary and secondary active transport "Vesicle loading is a...
O D Side-by-Side The thermodynamics of vesicle loading: Primary and secondary active transport "Vesicle loading is another interesting application of thermodynamics. Think about it. How do neurons form these highly concentrated vesicles full of, say. Ach? It turns out that neurons use a two-step system. First, neurons use the Gibb's free energy from hydrolyzing ATP to pump H+ ions into the vesicle using an H+/ATPase. Given the provided information, and assuming the vesicular membrane potential is 20 mV (positive inside the vesicle). how much Gibb's free energy is available to move Ach into the vesicle per mole of H+ ions that are antiported? Note that the positively charged proton is moving our of the vesicle. So, what is the change in potential going front inside to outside the vesicle? kJ/mol As you know, intracellular pH is approximately 7.20, but vesicular pH can get as low as 5.50 due to the influx of H+ jons. The influx of H+ ions also generates a membrane potential of about 20 mV, wherein the inside of the vesicle is positive relative to the cytoplasm around the vesicle. In the second step, an H Ach antiporter moves one molecule of Ach into the vesicle in exchange for moving two Htions back into the cytoplasm."