^1 Given oxidative phosphorylation, how can the cell utilize the inner-membrane
ID: 180541 • Letter: #
Question
^1 Given oxidative phosphorylation, how can the cell utilize the inner-membrane space to balance coupled transport to drive movement of ions across the membrane without wasting ATP; how does the cell establish a concentration gradient of ions to effectively lower the pH without compromising other organelle or cytosolic physiological functions?^2 How does active and passive transport facilitate the chemismotic coupling between transporting H+ across the membrane and generating energy from H+ movement into the lumen?Explanation / Answer
Inner-membrane space is a region between outer ans inner membranes present in the mitochondria. This is the region where oxidative phosphorylation happens. Inner membrane contain respiratory electron carriers (complexes I-IV), ADP-ATP translocase, ATP synthase and other membrane transporters. The inner membrane is impermeable to most small molecules and ions, including H+. As the electron transfers from one complex to another, the proton pump uses this energy to pump protons into inner mitochondrial space. This causes proton gradient across the membrane. This proton gradient used to synthesize ATP.
The chemiosmotic theory proposes that energy from electron transport drives an active transport system, which pumps protons out of the mitochondrial matrix into the intermitochondrial space. This action generates electrochemical gradient for protons, with a lower pH value outside the inner mitochondrial membrane than inside. The protons on the outside have a thermodinemic tendency of flow back into the matrix so as to equalize pH. When protons do flow back into the matrix, the energy is dissipated, some of it being used to drive the synthesis of ATP.
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