The electron transport chain is a process that occurs after kreb's cycle. During kreb's cycle two important molecules are produced:NADH+H+ and FADH2. Those molecules store electrons. The electron transport chain is made of different components that accept the electron(reduce) and give them to the next component of the etc(oxidize). The first part of the electron transport chain is the complex I(NADH-oxido-reductase). This complex accepts electrons from NADH the substance that is recieves the electrons(is reduced) is called flavo-adenine-mononucleotide(FAD) when it is reduced it becomes FADH2. When this redox process occurs some of the energy in the electrons is lost. This energy is used by the first complex to pump hydrogen ions inside the inter-membrane space. FADH2 is then oxidized and it gives the electron to coenzyme-Q(a non proteic component of the electron transport chan that carries electrons). The second complex is called FADH-oxydo reductase it receives electrons from FADH2. This complex doesn't pump hydrogen ions. The protons from FADH2 are given off to coenzyme-Q. Coenzyme-Q gives the electrons it received to the third complex(cytochrome B). This substance contains iron which can either be in the reduced form when it receives an electron(Fe++) also called ferrous form or in the oxidized form (Fe+++) after it gave off electrons. The energy is also used in this complex to pump hydrogen ions from the mitochondrial matrix to the inter-membrane space. Cytochrome C is the next component in the E.T.C. that also has iron that is in ferrous form when it receives an electron and in ferric form when it gives it to the next component, complex IV(cytochrome aa3). Here iron is again reduced(Fe⁺⁺⁺+e⁻-->Fe⁺⁺) and then oxidized but this time the electrons are received by O₂ that has been inhaled by the orgainsm. Molecular oxygen becomes atomic oxygen that is highly reactive and reacts fast with hydrogen protons in the matrix to form water. Now comes the question:"what happens to the protons that have been pumped into the inter-membrane space?" This process was explained by Mitchell in 1961. The protons create and electrical gradient(because the inter-membrane space is more positive than the matrix because of the positive charge) and a chemical gradient(there is a higher concentration of protons). Those protons need to flow back in. There is a protein in the inner membrane called ATP-synthase. When protons pass through, the energy they release is used for this reaction to occur(ADP+H3PO4(inorganic phosphate)--->ATP+H2O).