1-Ch1 Chemical & Physical Foundations Copy 5 PDF

Energy Coupling Links Reactions in Biology free-energy change, ∆G = amount of energy available to do work – always less than the theoretical amount of energy released in closed systems, chemical reactions proceed spontaneously until equilibrium is reached  Disc...

Energy Coupling Links Reactions in Biology free-energy change, ∆G = amount of energy available to do work – always less than the theoretical amount of energy released in closed systems, chemical reactions proceed spontaneously until equilibrium is reached  Discussion / Question If under a given set of conditions, the reaction A → B occurs with ∆G = –14 kJ/mol and the reaction C → B occurs when ∆G = +16 kJ/mol, then: A. the conversion of C to A is freely reversible. B. the conversion of A to C is exergonic. C. A and C can never be at equilibrium, even under different reaction conditions. D. the conversion of A to C is entropically driven. Keq and ∆G° are Measures of a Reaction’s Tendency to Proceed Spontaneously For the reaction, aA + bB ⎯⎯ → cC + dD The equilibrium constant, Keq, is given by Ceq  Deq c d Keq =  Aeq  Beq a b Where [A]eq is the concentration of A, [B]eq the concentration of B, and so on, when the system has reached equilibrium.  Mass-Action Ratio, Q mass-action ratio, Q = ratio of product concentrations to reactant concentrations at a given time – can be calculated to determine how far the reaction is from equilibrium  Question ATP breakdown yields ADP and inorganic phosphate (Pi). The Keq for the reaction is 2 × 105 M: If measured cellular concentrations are [ATP] = 15 mM, [ADP] = 1.5 mM, and [Pi] = 15 mM, is this reaction at equilibrium in living cells? A. Yes, because Q = Keq. B. No, because Q = Keq. C. Yes, because Q