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In heterogeneous electron transfer, an electron moves between a chemical species present in solution and the surface of a solid such as a semi-conducting material or an electrode. Theories addressing heterogeneous electron transfer have applications in electrochemistry and the design of solar cells.
An electron transport chain (ETC [1]) is a series of protein complexes and other molecules which transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples this electron transfer with the transfer of protons (H + ions) across a membrane.
NADH and FADH 2 undergo oxidation in the electron transport chain by transferring an electrons to regenerate NAD + and FAD. Protons are pulled into the intermembrane space by the energy of the electrons going through the electron transport chain. Four electrons are finally accepted by oxygen in the matrix to complete the electron transport chain.
Water-splitting process: Electron transport and regulation. The first level (A) shows the original Kok model of the S-states cycling, the second level (B) shows the link between the electron transport (S-states advancement) and the relaxation process of the intermediate S-states ([YzSn], n=0,1,2,3) formation
The chain of redox reactions driving the flow of electrons through the electron transport chain, from electron donors such as NADH to electron acceptors such as oxygen and hydrogen (protons), is an exergonic process – it releases energy, whereas the synthesis of ATP is an endergonic process, which requires an input of energy.
The carriers pass electrons to the electron transport chain (ETC) in the inner mitochondrial membrane, which in turn pass them to other proteins in the ETC. The energy at every redox transfer step is used to pump protons from the matrix into the intermembrane space, storing energy in the form of a transmembrane electrochemical gradient.
In cellular biology, active transport is the movement of molecules or ions across a cell membrane from a region of lower concentration to a region of higher concentration—against the concentration gradient. Active transport requires cellular energy to achieve this movement.
The transfer of electrons from a donor molecule to an acceptor molecule can be spatially separated into a series of intermediate redox reactions. This is an electron transport chain (ETC). Electron transport chains often produce energy in the form of a transmembrane electrochemical potential gradient.