Which complex in the electron transport chain does not contribute to the proton gradient? Why not? Solution Ans - An electron transport chain ( ETC ) is a series of complexes that transfer electrons from electron donors to electron acceptors via redox (both reduction and oxidation occurring simultaneously) reactions, and couples this electron transfer with the transfer of protons (H + ions) across a membrane. This creates an electrochemical proton gradient that drives the synthesis of adenosine triphosphate (ATP), a molecule that stores energy chemically in the form of highly strained bonds. The molecules of the chain include peptides, enzymes (which are proteins or protein complexes), and others. The final acceptor of electrons in the electron transport chain during aerobic respiration is molecular oxygen although a variety of acceptors other than oxygen such as sulfate exist in anaerobic respiration. The four complexes involved in electron transport chain are Complex II does not contribute to proton gradient in electron transport chain. This complex oxidizes succinate, which is produced in TCA cycle, and transfers electrons to ubiquinone. This complex is not associated with any proton gradient. .

1. Which complex in the electron transport chain does not contribute to the proton gradient? Why
not?
Solution
Ans - An electron transport chain ( ETC ) is a series of complexes that transfer electrons from
electron donors to electron acceptors via redox (both reduction and oxidation occurring
simultaneously) reactions, and couples this electron transfer with the transfer of protons (H +
ions) across a membrane. This creates an electrochemical proton gradient that drives the
synthesis of adenosine triphosphate (ATP), a molecule that stores energy chemically in the form
of highly strained bonds. The molecules of the chain include peptides, enzymes (which are
proteins or protein complexes), and others. The final acceptor of electrons in the electron
transport chain during aerobic respiration is molecular oxygen although a variety of acceptors
other than oxygen such as sulfate exist in anaerobic respiration. The four complexes involved in
electron transport chain are
Complex II does not contribute to proton gradient in electron transport chain. This
complex oxidizes succinate, which is produced in TCA cycle, and transfers electrons to
ubiquinone. This complex is not associated with any proton gradient.