Electron Transport Chain

Study Notes

Specialized set of electron carriers located in the inner mitochondrial membrane, which facilitates the flow of electrons from different fuels to oxygen.
Consists of five separate protein complexes (I, II, III, IV, and V) in the inner mitochondrial membrane.
Each complex contains part of the electron transport chain, except for Complex V, which catalyzes ATP synthesis.

With the exception of coenzyme Q, all members of the chain are proteins.
These proteins may function as enzymes, contain iron, be coordinated with a porphyrin ring, or contain copper.

Formation of NADH: NAD+ is reduced to NADH by dehydrogenases, which remove two hydrogen atoms from their substrate.
NADH dehydrogenase: The free proton and hydride ion are transferred to NADH dehydrogenase (Complex I), which has a tightly bound molecule of Flavin mononucleotide (FMN) that accepts the two hydrogen atoms.
Coenzyme Q: Accepts hydrogen atoms from FMNH2 and FADH2, and transfers electrons to Complex III.
Cytochromes: Electrons are passed along the chain from coenzyme Q to cytochromes bc1 (Complex III), c, and a + a3 (Complex IV).
Cytochrome a + a3: This complex can react directly with molecular oxygen, forming water and releasing free energy.

Free energy is released as electrons are transferred along the electron transport chain from an electron donor to an electron acceptor.
The standard reduction potential (E) of a redox pair determines the tendency of the reductant member to lose electrons and the oxidant member to accept electrons.

Concerns the transfer and utilization of energy in biologic systems, focusing on the initial and final energy states of reaction components.
Enthalpy (ΔH): Measure of the change in heat content of reactants and products.
Entropy (ΔS): Measure of the change in randomness or disorder of reactants and products.
Free Energy Change (ΔG): Measure of the energetic feasibility of a chemical reaction, predicting the direction in which a reaction will spontaneously proceed.

ATP consists of a molecule of adenosine with three phosphate groups attached.
The standard free energy of hydrolysis of ATP, ΔG°, is approximately -7.3kcal/mol for each of the two terminal phosphate groups, making ATP a high-energy phosphate compound.