Chapter 13.1: Bioenergetics and Thermodynamics CHEM 7784 Biochemistry Professor Bensley

Introduction and Chapter 13.1 Bioenergetics and Thermodynamics –Differences between metabolic, catabolic, and anabolic processes –Thermodynamic applications to metabolic processes Today’s Objectives: To learn and understand the

Bioenergetics and Thermodynamics Bioenergetics – the quantitative study of energy transductions (changes from one form to another) First Law of Thermodynamics – conservation of energy Second Law of Thermodynamics – universe always tends towards increasing disorder

Laws of Thermodynamics Apply to Living Organisms In order to maintain organization within the themselves, living systems must be able to extract useable energy from the surrounding, and release useless energy (heat) back to the surrounding (Open systems)

Mathematical Relationships ∆G = ∆H - T∆S Standard free-energy change (∆G 0 ) – standard conditions (298K, 1 atm, [1M] initial for both reactants and products) Biochemical standard state says that [H + ] = and [H 2 O] = 55.5 M Physical constants based on biochemical standard state are written with a prime such as ∆G ’0 and K ’ eq

Mathematical Relationships ∆G ’0 = -RT ln K ’ eq

Mathematical Relationships ∆G is a constant but ∆G ’0 is a function of concentrations and temperature ∆G = ∆G ’0 + RT ln [C] c [D] d [A] a [B] b Spontaneity of a reaction is determined by value of ∆G not ∆G ’0 Some thermodynamically favorable reactions do not occur at measurable rates (combustion of firewood) so they need to be catalyzed (enzymes)

Mathematical Relationships Standard free-energy changes are additive in the case of two sequential reactions Because of this, the idea of coupling a highly exergonic reaction to an thermodynamically unfavorable one happens Example (Glucose 6-phosphate formation) Equilibrium constants are multiplicative in the case of two sequential reactions

Hydrolysis Reactions tend to be Strongly Favorable (Spontaneous)

Complete Oxidation of Reduced Compounds is Strongly Favorable This is how chemotrophs obtain most of their energy In biochemistry the oxidation of reduced fuels with O 2 is stepwise and controlled Recall that being thermo- dynamically favorable is not the same as being kinetically rapid