answers.input_text: short
answers.span_text: electron donors
questions: where does the electron transport chain get its electrons from
name: Electron transport chain
contexts: 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 .