All the contents of the electron transport chain are embedded in or attached to the inside mitochondrial membrane. In the matrix, NADH deposits electrons at complicated I, turning into NAD+ and releasing a proton into the matrix. FADH2 in the matrix deposits electron at facility II, turning into FAD and releasing 2 H+. The electron from Complexes I and also II room passed to the little mobile transport Q. Q transports the electrons to facility III, which climate passes them to Cytochrome C. Cytochrome C passes the electrons to complex IV, which climate passes them to oxygen in the matrix, forming water. That takes two electrons, 1/2 O2, and also 2 H+ to type one water molecule. Complexes I, III, and also IV use energy released as electrons move from a greater to a lower energy level come pump protons out of the matrix and into the intermembrane space, generating a proton gradient.

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All of the electrons that go into the transfer chain come indigenous NADH and also FADH2 molecules created during earlier stages of to move respiration: glycolysis, pyruvate oxidation, and also the citric acid cycle.


NADH is very an excellent at donating electrons in redox reaction (that is, its electrons are at a high power level), so it have the right to transfer that electrons directly to complicated I, turning back into NAD+. As electrons move through facility I in a collection of redox reactions, power is released, and also the complicated uses this energy to pump proton from the matrix into the intermembrane space.


FADH2 no as great at donating electrons together NADH (that is, that electrons room at a lower energy level), so that cannot transfer its electron to facility I. Instead, the feeds them right into the carry chain through facility II, i m sorry does not pump protons across the membrane. Because of this, a FADH2 molecule causes fewer protons to be pumped (and contributes much less to the proton gradient) 보다 an NADH molecule.

Complex I. NADH transfers its electrons to complicated I. Facility I is rather large, and the part of it the receives the electron is a flavoprotein, an interpretation a protein through an attached necessary molecule dubbed flavin mononucleotide (FMN). FMN is a prosthetic group, a non-protein molecule strictly bound to a protein and required for its activity, and also it’s FMN that in reality accepts electron from NADH. FMN overcome the electrons to another protein inside complex I, one that has iron and sulfur bound to it (called an Fe-S protein), i m sorry in turns transfers the electron to a small, cell phone carrier dubbed ubiquinone (Q in the chart above).


Complex II. Choose NADH, FADH2 store its electrons in the electron transport chain, yet it does so via complicated II, bypassing complicated I entirely. As a matter of fact, FADH2 is a component of complex II, as is the enzyme the reduces it during the citric acid cycle (succinate dehydrogenase). Uneven the various other enzymes of the cycle, it’s installed in the inner mitochondrial membrane. FADH2 move its electrons to iron-sulfur protein within complicated II, i m sorry then pass the electrons to ubiquinone (Q), the very same mobile carrier the collects electron from complex I.


Beyond the very first two complexes, electrons from NADH and also FADH2 travel specifically the exact same route. Both complex I and facility II happen their electrons to a small, mobile electron carrier referred to as ubiquinone (Q), i beg your pardon is reduced to kind QH2 and travels through the membrane, moving the electrons to complicated III. Together electrons move through complicated III, an ext hydrogen ions are pumped across the membrane, and also the electrons space ultimately yielded to one more mobile carrier dubbed cytochrome C (cyt C). Cyt C dead the electrons to facility IV, wherein a final batch the hydrogen ions is pumped across the membrane. Complex IV overcome the electrons to O2, which splits right into two oxygen atoms and also accepts proton from the matrix to type water. Four electrons are forced to alleviate each molecule that O2, and two water molecule are formed in the process.


Complex III. Like complex I, complicated III includes an iron-sulfur (Fe-S) protein, yet it likewise contains 2 proteins of another type, well-known as cytochromes. Cytochromes space a household of related proteins that have heme prosthetic groups containing stole ions. In complex III, electrons room passed from one cytochrome to an iron-sulfur protein to a second cytochrome, then ultimately transferred the end of the complex to a cell phone electron carrier (cytochrome C). Like complicated I, complex III pumps protons from the matrix right into the intermembrane space, contributing come the hydrogen ion concentration gradient.


Complex IV. From complicated III, cytochrome C delivers electrons to the last complicated of the electron carry chain, complicated IV. There, the electrons room passed with two more cytochromes, the 2nd of which has actually a an extremely interesting job: through the help of a adjacent copper ion, that transfers electron to O2 separating oxygen to form two molecule of water. The protons provided to kind water come native the matrix, contributing to the hydrogen ion gradient, and complex IV also pumps proton from the procession to the intermembrane space.


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Key Points

• NADH and also FADH2 pass their electron to the electron carry chain, transforming back right into NAD+ and also FAD. This is important due to the fact that the oxidized forms of these electron carrier are supplied in glycolysis and also the citric acid cycle and also must be easily accessible to save these procedures running.

• The carry chain builds a proton gradient across the inner mitochondrial membrane, through a higher concentration that hydrogen ions in the intermembrane room and a reduced concentration in the matrix. This gradient represents a stored kind of energy and also it deserve to be supplied to make ATP.

• NADH is far better at donating electrons in oxidization reactions 보다 FADH2, meaning that FADH2 molecules cause fewer proton to be pumped 보다 NADH molecules.

Cytochromes are a family of connected proteins that have heme prosthetic teams containing iron ions. Electrons space passed indigenous one cytochrome to an iron-sulfur protein come a 2nd cytochrome, then lastly transferred out of the complicated to a mobile electron carrier cytochrome C, which can only carry one electron at a time.

Key Terms

Electron deliver chain: A collection of protein complexes installed in the inner mitochondrial membrane that expropriate electrons indigenous electron carriers in order come pump protons right into the intermembrane space.

Electron carriers: has NADH and FADH2, which happen the electron acquired throughout early stages of cellular respiration come the protein in the electron deliver chain.

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Electrochemical gradient: The combination of a concentration gradient and electrical gradient because of an unequal distribution of ions throughout a membrane.