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Step 5: In this step, succinic acid is oxidized as it gives up 2 hydrogen atoms and 2 high energy electrons to a type of electron carrier called FAD. The reduction of FAD yields FADH₂. FADH₂ is already imbedded in the electron transport chain, as you will learn about later. It deposits the electrons and the hydrogen ions into the electron transport chain. The enzyme responsible for catalyzing this reaction is succinate dehydrogenase.