Ohm\'s law states V = I R; Instead of resistance, one can express this in terms

Question

Ohm's law states V = I R; Instead of resistance, one can express this in terms of conductance g. V = I/g or I = V g. The measured value of "conductance per unit area" of sodium channels is 0.13 ohm^-1 m^-2 in the resting state of giant axons. The concentration of sodium inside the cell is 12mM while outside the cell is 145mM; the membrane voltage is -90 mV. If pumps are suddenly turned off, sodium will rush in. Find the current per unit area carried by sodium ions. Re-express your answer as current per unit length along the giant axon assuming a diameter of 1 mm. Make a rough estimate of how long it will take for the internal concentration of sodium to match that of the outside. Assume current is constant through the whole time for this estimate. Action potential lasts for about a few millisecs. Assume that during the action potential sodium's conductance rises transiently to 100 ohm^-1 m^-2. Comment on how the time calculated in c compares with the time that action potential lasts for. Give an example of importance of bioelectricity/charges in any process except action potential generation and propagation.

Explanation / Answer

Apart from action potential generation and propagation, bioelectricity is also useful in synthesis of ATP in mitochondria through the process of chemiosmosis. During the process of transfer of electrons through the electron transport chain , electrons are transported into the intermembrane space of the mitochondria. Adding to the electrochemical potential produced by redox-driven proton transport the electrochemical energy inherent in the difference in proton concentration and separation of charge across the inner mitochondrial membrane—the proton-motive force—drives the synthesis of ATP as protons flow passively back into the matrix through a proton pore associated with ATP synthase. The protein complexes involved in the process of electron transfer located in the mitochondrial inner membrane are responsible for ejecting or pumping electrons in the mitochondrial inter membrane space. This large positive charge in the mitochondrial inter membrane space generates a concentration & proton gradient which returns back into the mitochondrial matrix through the F1/F0 ATP synthase enzyme which generates one molecule of ATP from ADP and inorganic phosphate in the matrix for transfer of 3H+ ions into the mitochondrial matrix from the inter-membrane space.

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