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Questions and Answers
What is the main concern of Bioenergetics?
What does the enthalpy (ΔH) measure?
What is the significance of a negative ΔG?
What is the term for a reaction that does not proceed spontaneously?
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What is the approximate ΔG° of ATP hydrolysis?
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Why is ATP called a high-energy phosphate compound?
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What is the function of ATP in bioenergetics?
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What is the significance of ΔG being zero?
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What is the term for the change in randomness or disorder of reactants and products?
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What is the term for a reaction that proceeds spontaneously?
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Study Notes
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.
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Description
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.