<P> Energy obtained through the transfer of electrons down the ETC is used to pump protons from the mitochondrial matrix into the intermembrane space , creating an electrochemical proton gradient ( ΔpH ) across the inner mitochondrial membrane ( IMM ) . This proton gradient is largely but not exclusively responsible for the mitochondrial membrane potential ( ΔΨ ) . It allows ATP synthase to use the flow of H through the enzyme back into the matrix to generate ATP from adenosine diphosphate ( ADP ) and inorganic phosphate . Complex I ( NADH coenzyme Q reductase ; labeled I ) accepts electrons from the Krebs cycle electron carrier nicotinamide adenine dinucleotide ( NADH ) , and passes them to coenzyme Q ( ubiquinone ; labeled Q ) , which also receives electrons from complex II ( succinate dehydrogenase ; labeled II ) . Q passes electrons to complex III ( cytochrome bc complex ; labeled III ) , which passes them to cytochrome c ( cyt c ) . Cyt c passes electrons to Complex IV ( cytochrome c oxidase ; labeled IV ) , which uses the electrons and hydrogen ions to reduce molecular oxygen to water . </P>
<P> Energy obtained through the transfer of electrons down the ETC is used to pump protons from the mitochondrial matrix into the intermembrane space , creating an electrochemical proton gradient ( ΔpH ) across the inner mitochondrial membrane ( IMM ) . This proton gradient is largely but not exclusively responsible for the mitochondrial membrane potential ( ΔΨ ) . It allows ATP synthase to use the flow of H through the enzyme back into the matrix to generate ATP from adenosine diphosphate ( ADP ) and inorganic phosphate . Complex I ( NADH coenzyme Q reductase ; labeled I ) accepts electrons from the Krebs cycle electron carrier nicotinamide adenine dinucleotide ( NADH ) , and passes them to coenzyme Q ( ubiquinone ; labeled Q ) , which also receives electrons from complex II ( succinate dehydrogenase ; labeled II ) . Q passes electrons to complex III ( cytochrome bc complex ; labeled III ) , which passes them to cytochrome c ( cyt c ) . Cyt c passes electrons to Complex IV ( cytochrome c oxidase ; labeled IV ) , which uses the electrons and hydrogen ions to reduce molecular oxygen to water . </P>
where do krebs ( step 2 ) and the etc ( step 3 ) occur
where do krebs ( step 2 ) and the etc ( step 3 ) occur
mitochondrial matrix
mitochondrial matrix