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Chapter 13
Principles of Bioenergetics
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Metabolism - Coordinated cellular activity - Sum of all the chemical transformations in organism
Chemical energy Precursor molecules Macromolecules
Specialized biomolecules
Catabolism Degradative phase Energy release (exergonic)
Anabolism Biosynthesis Energy input (endergonic)
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Three types of metabolic pathways
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13.1 Bioenergetics and Thermodynamics
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Bioenergetics
Bioenergetics The quantitative study of…
Cellular energy transduction Nature and function of the chemical processes for
energy transductions
Fundamental laws in thermodynamics governing bioenergetics First law : Energy conservation
Second law: Increase in entropy
Living Orgamism 1. Metabolism 2. Reproduction Energy: work to survive and reproduce
Energy transduction in biological system
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Free Energy Change for Biological Reactions
Thermodynamic quantities describing the energy changes in chemical reaction Gibbs free energy, G
The amount of energy capable of doing work during a reaction at constant T and P
PositiveG : endergonic NegativeG : exergonic, spontaneous reaction
Enthalpy, H The heat content of the reacting system Number & kinds of chemical bonds in the reactants and products PositiveH : endothermic NegativeH : exothermic
Entropy, S Quantitative expression for the randomness or disorder in a
system G = H –TS Cells use free energy for reactions
Energy source Heterotrope :Nutrient Autotrope: Solar energy
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Standard Free Energy Change vs. Equilibrium Constant
aA + bB cC + dD Equilibrium constant [Ceq]c [Deq]d
[Aeq]a [Beq]b
Go : standard free energy change (J/mol) 298K=25oC, 1M of initial reactants and products,1 atm (101.3 kPa)
Standard transformed constants pH 7, 55.5M water, 1mM Mg2+ (ATP as reactant) G’o, K’eq
G’o = -RT ln K’eq
Spontaneous reaction K’’
eq >1 Go : negative
Keq =
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G’o for some representative chemical reactions
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G’o are additive
Sequential chemical reactions (1) A B : G’1o, K’eq1
glucose + Pi G-6P + H2O ; G’ o = 13.8 kJ/mol
(2) B C : G’2o , K’eq2
ATP + H2O ADP + Pi ;G’ o = -30.5 kJ/mol
(1) + (2) : A C : G’1o + G’1o, K’eq1 X K’eq2
ATP + glucose ADP + Pi ; G’ o = -16.7 kJ/mol
Coupling of endergonic and exergonic reaction to make exergonic reaction
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13.2 Chemical logic & common biochemical reactions
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General categories of biochemical reactions
Reactions that make or break C-C bonds
Internal rearrangements/ isomerizations/
eliminations
Free-radical reactions
Group transfers
Oxidation-reductions
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Two basic chemical principle
Covalent bond breakdownCovalent bond breakdown Nucleophile/ electrophileNucleophile/ electrophile
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Formation & breakdown of C-C bonds
Carbanion stabilization - by carbonyl group - by imine - by metal ions or general acid catalyst
Common reactions mediated by carbonyl-stabilized carbanions
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Formation & breakdown of C-C bonds
Carbocation in C-C formation
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Internal rearrangements, Isomerizations, eliminations
Rearrangements/ isomerizations
Elimination reactions
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Free radical reactions
Free radical-initiated decarboxylation
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Group transfer reactions
Acyl group transfer
Phosphoryl group transfer
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Oxidation-reduction reactions
Oxidation - Lose of 2 e- and 2 H+ ; dehydrogenations (dehydrogenases) - Covalent addition of oxygen to carbon atom (oxidases/ oxygenases)
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13.2 Phosphoryl Group Transfers and ATP
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Free-Energy Change for ATP Hydrolysis
Chemical basis for large & negative G’o for ATP hydrolysis Relief of electrostatic repulsion Resonance stabilization of released Pi
Ionization of ADP2- to release H+
Greater degree of solvation of the Pi and ADP than ATP
Products concentrations are far below the concentration at equilibrium mass action favors hydrolysis of ATP
Gp : phosphorylation potential in the cell in human erythrocyte Gp = G’o + RT ln [ADP] [Pi]/ [ATP] = -30.5 kJ/mol - 21 kJ/mol = -52 kJ/mol
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Free-Energy Change for ATP Hydrolysis
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Other High Energy Compounds : Phosphorylated Compounds
Phosphoenolpyruvate Stabilization of product by
tautomerization G’o = - 61.9 kJ/mol
1,3-bisphosphoglycerate Stabilization by ionization of a
direct product (3-phosphoglycerate) Resonance stabilization of the
ionized product G’o = - 49.3 kJ/mol
Phosphocreatine Resonance stabilization of a
product G’o = - 43.0 kJ/mol
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Other High Energy Compounds : Thioesters
Thioester S instead of O in the ester bond Resonance stabilization of hydrolysis product Less resonance stabilization than ester
Large free energy difference between thioester and the hydrolysis product