Part C – Proton gradient formation and ATP synthesis
top left pink: emptybottom left: site of H+ releasetop right pink: site of ATP synthesisleft blue: H+ pumped across membranemiddle blue: emptyright blue: H+ diffuses across membrane
1. Explain the process of electron transport chain in mitochondria.
The electron transport chain (ETC) is a series of electron carriers located on the inner mitochondrial membrane. During oxidative phosphorylation, the ETC plays a vital role in generating ATP.
The ETC is comprised of various protein complexes, including NADH dehydrogenase, cytochrome c reductase, cytochrome c oxidase, and ATP synthase. Electrons from NADH and succinate are transferred to the ETC by respiratory complex I and complex II, respectively. These electrons are then passed through the various protein complexes, effectively pumping protons out of the mitochondrial matrix and into the intermembrane space.
The final electron acceptor in the ETC is oxygen, which reacts with protons and electrons to form water. This generates a proton gradient across the inner mitochondrial membrane, with a high concentration of protons in the intermembrane space and a low concentration in the matrix.
2. How is the proton motive force generated in mitochondria?
The proton motive force (PMF) is generated by the movement of protons across the inner mitochondrial membrane. This movement occurs as a result of the electron transport chain (ETC), specifically during the transfer of electrons down the chain. As electrons pass through the ETC, protons are pumped from the mitochondrial matrix to the intermembrane space, creating a concentration gradient of protons.
The PMF consists of both electrical and chemical components. The electrical component arises from the separation of charges across the membrane, while the chemical component results from the gradient in proton concentration. The PMF is crucial in driving ATP synthesis, as the energy from the PMF is harnessed by ATP synthase to form ATP.
3. What is the role of ATP synthase in the process of ATP synthesis in mitochondria?
ATP synthase is a complex enzyme responsible for the synthesis of ATP during oxidative phosphorylation in mitochondria. ATP synthase is located on the inner mitochondrial membrane and is comprised of two components – the F0 unit, which sits within the membrane, and the F1 unit, which protrudes into the mitochondrial matrix.
As protons move down the concentration gradient from the intermembrane space into the matrix through the F0 unit, this causes the rotor subunit to rotate within the membrane. The movement of the rotor causes conformational changes in the F1 unit, which in turn facilitates the synthesis of ATP. ADP and inorganic phosphate are brought into the matrix by the adenine nucleotide translocator, and these are then used to form ATP by ATP synthase.
Overall, ATP synthase functions as a molecular motor, harnessing the energy from the proton motive force to drive the synthesis of ATP.
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