Questions and Answers
What is the overall reaction catalyzed by fatty acid synthetases?
Fatty Acid + ATP + CoA → Fatty Acyl-CoA + AMP + PPi
Which enzyme prevents the Right to Left reaction in the conversion of fatty acids to fatty acyl-CoA?
Oxidation is the gain of electrons.
False
What does a positive DEo indicate in a redox reaction?
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The Nernst equation relates free energy difference to the difference in ____________ potentials.
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Calculate the free energy change (DG'o) for the redox reaction between the NAD/NADH, H+ couple and the Ferredoxin (+3)/Ferredoxin (+2) couple.
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Which of the following statements is true regarding the reduction potential?
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Write the balanced redox reaction using NAD+/NADH and Ferredoxin.
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What is the form of Gibb’s equation that expresses free energy change?
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A positive standard free energy change (ΔGº′) indicates a spontaneous reaction.
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One food calorie is equivalent to _____ chemical calories.
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What is indicated by the Gibbs free energy change equation G′ = ΔGº′ + RT ln Q?
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Which of the following are considered high energy metabolites? (Select all that apply)
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What is the main reason for the complexity in intermediary metabolism?
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Match the following food types with their caloric values (kcal/g):
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Catabolism is energy-consuming while anabolism is energy-yielding.
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What is the main role of feedback inhibition in metabolic pathways?
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Study Notes
Learning Objectives
- Formulate Gibb's equation to express free energy change in terms of reactant and product concentrations.
- Define chemical equilibrium and relate Keq values to reactant and product energies.
- Identify conditions for spontaneous reactions defined by positive standard free energy change (ΔGº′).
- Calculate nutritional values of food based on carbohydrate, fat, and protein content.
- Distinguish between catabolism (energy-yielding) and anabolism (energy-consuming) processes.
- Explain significance of additive nature of free energy changes in metabolic reactions.
- Define “high energy metabolite” and list products formed from ATP cleavage.
- Use reduction potentials and Nernst equation to deduce electron flow direction in redox reactions.
Thermodynamics and Gibbs Equation
- First Law of Thermodynamics: Energy is conserved; it cannot be created or destroyed, only transformed.
- Gibbs Free Energy (ΔG): Indicates the spontaneity of a reaction; ΔG = Gproducts - Greactants. Spontaneous reactions have negative ΔG.
- Modified Gibbs Equation: ΔG' = ΔGº′ + RT ln Q; utilizes Q (product/reactant ratio) and standard free energy change (ΔGº′).
- Equilibrium Constant (Keq): Relates free energy to product and reactant concentrations; Keq = e^(-ΔGº′/RT).
Chemical Equilibrium
- Equilibrium Defined: A dynamic balance in energy distribution between reactants and products.
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Keq Interpretation:
- Keq = 1: Reactants and products have equal energy (ΔGº′ = 0).
- Keq < 1: Products have higher energy than reactants, requiring energy input (ΔGº′ > 0).
- Keq > 1: Reactants have higher energy than products, spontaneous with energy release (ΔGº′ < 0).
Food Energetics
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Caloric Values:
- Fats: 9 kcal/g
- Carbohydrates: 4 kcal/g
- Proteins: 4 kcal/g
- Alcohol: 7 kcal/g
Metabolic Pathways
- Intermediary Metabolism: Series of chemical reactions managing cellular materials and energy resources.
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Anabolic vs. Catabolic Pathways:
- Anabolic: Builds complex molecules, energy-consuming, diverging pathways.
- Catabolic: Breaks down molecules, energy-yielding, converging pathways.
Enzyme Function and Pathway Directionality
- Metabolic pathways are directionally irreversible, typically involving unique enzymes for each step.
- The end product has minimal resemblance to the starting material, distinguishing catabolic and anabolic pathways.
Free Energy Change in Metabolism
- Additive Nature of Free Energy Changes: Cells can couple endergonic and exergonic reactions to drive biological processes.
- Example: Glucose phosphorylation coupled with ATP hydrolysis illustrates combined energy changes.
- TCA cycle showcases cumulative free energy changes leading to spontaneous reactions despite individual step favorability.
Energy Sources and Metabolism
- Hydrocarbons (fats, proteins, carbohydrates) serve as primary energy substrates in metabolism.
- Similar to combustion engines, exothermic oxidation of hydrocarbons releases energy for cellular work.
These notes summarize essential concepts and details relating to metabolism and bioenergetics, preparing students to understand fundamental biochemical processes.### Energy Release in Metabolism
- Combustion engines utilize the energy from hydrocarbons reacting with oxygen, but biological systems release energy gradually through multiple chemical steps.
- Direct oxidation of glucose (656 kcal/mol) and fatty acids (2338 kcal/mol) is too intense for biological life; instead, energy is released in small increments (10-15 kcal/mol).
Energy Conversion Process
- Dietary nutrients provide energy in reducing equivalents (e- and H+) that feed into carrier molecules, ultimately transferring to oxygen.
- Approximately 60% of energy lost as heat, 40% conserved as ATP (adenosine triphosphate).
Importance of Activated Intermediates
- Molecules must be converted to activated intermediates for biochemical reactions, requiring 2-3 steps for activation.
- ATP hydrolysis is highly exergonic (ΔG°' = -7.3 kcal/mol) but concentrations remain low, necessitating regulatory mechanisms to maintain ATP levels above equilibrium.
Energy Charge and Metabolism
- High ATP/NADH ratios indicate a high-energy charge favoring anabolism; low ratios favor catabolism.
- Feedback inhibition regulates enzyme activity, preventing unnecessary production of metabolic intermediates.
Role of Nucleotide Triphosphates (NTPs)
- NTPs consist of a nitrogen base, ribose, and three phosphates linked by phosphoanhydride bonds.
- Hydrolysis of ATP releases significant energy (-7.3 kcal/mol) but ATP is not the highest energy metabolite.
Hierarchy of High-Energy Metabolites
- Hydrolysis free energy of key metabolites:
- Phosphoenolpyruvate: -14.8 kcal/mol
- Phosphocreatine: -12.0 kcal/mol
- 1,3-bisphosphoglycerate: -11.8 kcal/mol
- ATP: -7.3 kcal/mol
- The highest energy metabolites drive endergonic reactions and include substrate-level phosphorylation.
Phosphoryl Transfer Reactions
- Enzymes involved in phosphoryl transfer:
- NTP Hydrolase: Transfers between NTP and water.
- NTP Kinase: Transfers between NTP and other molecules.
- Nucleotidyl Transferase: Transfers nucleotidyl groups between NTP and other molecules.
Activation of Metabolites
- Fatty acid activation is a two-step reaction involving ATP and CoA, leading to the formation of fatty acyl-CoA, a high-energy metabolite.
- The irreversible nature of conversion is maintained by pyrophosphatases which cleave pyrophosphate (PPi).
Redox Reactions and Energy Flow
- Oxidation (electron loss) releases energy; reduction (electron gain) consumes energy.
- Standard reduction potential (E°) indicates the affinity of a metabolite for electrons, determining the direction of redox reactions.
Calculating Free Energy Changes
- The Nernst equation relates free energy to reduction potentials of redox pairs; a positive free energy change indicates a thermodynamically favored reaction.
- Example calculations illustrate the balancing of redox reactions using regenerative potential values of various couples, such as NAD/NADH and ferredoxin.
Practical Applications
- The interplay of NTPs in cellular processes ensures energy transfer to carry out essential biological functions, emphasizing the complex nature of metabolic pathways.
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Description
Understanding Gibbs' equation, chemical equilibrium, and equilibrium constants in bioenergetics and metabolism.
