Electron Transport Chain

Electron Transport Chain

• 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.

Electron Transport Chain Components

• 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.

Reactions of the Electron Transport Chain

• 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 Release during Electron Transport

• 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.

Bioenergetics/Biochemical Thermodynamics

• 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 as an Energy Carrier

• 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.

Quiz on the electron transport chain, a set of electron carriers in the inner mitochondrial membrane that facilitate the flow of electrons from different fuels to oxygen.