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Questions and Answers
What is the stepwise transfer mechanism of proton and hydride in dehydrogenases?
What is the stepwise transfer mechanism of proton and hydride in dehydrogenases?
What is the role of NAD and NADP?
What is the role of NAD and NADP?
What is the function of FMN and FAD?
What is the function of FMN and FAD?
What is the reaction mechanism of NAD and NADP?
What is the reaction mechanism of NAD and NADP?
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What is the characteristic of flavin nucleotides?
What is the characteristic of flavin nucleotides?
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What is the function of flavoproteins?
What is the function of flavoproteins?
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What is the significance of flavin cofactors?
What is the significance of flavin cofactors?
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What is the characteristic of ubiquinone?
What is the characteristic of ubiquinone?
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What is the role of iron-sulfur proteins?
What is the role of iron-sulfur proteins?
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What is the reaction of NAD and NADP after reduction?
What is the reaction of NAD and NADP after reduction?
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Study Notes
Thermodynamics and Bioenergetics
- The equation ΔG = ΔH - TΔS relates changes in free energy, enthalpy, and entropy under constant temperature and pressure conditions.
- ΔH is negative for exothermic reactions, and ΔS is positive for reactions that increase system randomness.
- Spontaneous reactions have a negative ΔG and do not require energy from their surroundings.
Energy Sources in Living Organisms
- Living organisms maintain internal order by taking free energy from their surroundings (nutrients or sunlight) and returning energy as heat and entropy.
- Cellular reactions involve the oxidation of glucose to CO2 and H2O, with the products being returned to the surroundings, increasing entropy.
Energy Requirements in Cells
- Living systems are isothermal, functioning at constant temperature and pressure.
- Cells acquire free energy from nutrient molecules, converting it into ATP and energy-rich compounds.
- Equilibrium is reached when the composition of a reacting system (reactants and products) stops changing.
Energy Coupling
- Chemical coupling of exergonic and endergonic reactions allows unfavorable reactions to occur.
- ATP reacts directly with metabolites that need "activation" in exergonic reactions, making the overall process spontaneous (ΔG < 0).
- Energy-requiring reactions are coupled to reactions that release free energy (exergonic).
Metabolism and Coupled Reactions
- Metabolism involves catabolism (degradative phase, releasing energy) and anabolism (building phase, requiring energy).
- Reactions are coupled through common intermediates, with ATP as an energy carrier.
- Many coupled reactions use ATP to generate a common intermediate.
Chemical Coupling Example
- Two reactions can be coupled through common intermediates (Pi and H2O) to form a spontaneous reaction (ΔG < 0).
- The strategy works only if ATP is continuously available.
Redox Pairs and Oxidation
- Reducing agents or reductants are electron-donating molecules, while oxidizing agents or oxidants are electron-accepting molecules.
- Conjugate redox pairs consist of an electron donor and an electron acceptor.
- Oxidation is often synonymous with dehydrogenation, catalyzed by dehydrogenases (oxidoreductases).
Electron Carriers
- Universal electron carriers include coenzymes (NAD+, NADP+, FMN, FAD) and proteins (iron-sulfur, cytochromes).
- NAD and NADP can dissociate from enzymes after reactions and undergo reversible reduction of the nicotinamide ring.
- Flavin nucleotides are tightly bound in flavoproteins, allowing single electron transfers and permitting the use of molecular oxygen as an ultimate electron acceptor.
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Description
Explore the relationship between thermodynamics and bioenergetics in living organisms, including the concepts of free energy, enthalpy, entropy, and spontaneous reactions.
