TThe oxidation of malate by NAD to form oxaloacetate is a highly endergonic reaction under standard conditions.AG° = +29 kJ mol¯¹ (+7 kcal mol¯¹)Malate + NAD+ = oxaloacetate + NADH + H+The reaction proceeds readily under physiological conditions.Why does the reaction proceed readily as written under physiological conditions?Endergonic reactions such as this occur spontaneously without the input of free energy.The steady-state concentrations of the products are low compared with those of the substrates.The reaction is pushed forward by the energetically favorable oxidation of fumarate to malate.O The NADH produced during glycolysis drives the reaction in the direction of malate oxidation.Assuming an [NAD* ]/[NADH] ratio of 8, a temperature of 25°C, and a pH of 7, what is the lowest [malate]/[oxaloacetate] ratioat which oxaloacetate can be formed from malate?[malate][oxaloacetate]=

Standards free energy change calculated at biochemical standards is called biochemical standard free energy change and is denoted by ΔG'° (delta G prime knot). K'eq is the equilibrium constant at biochemical standards and is related to biochemical standard free energy change:ΔG'° = -R T ln K'eqWhere R is the universal gas constant equal to 8.314 J mol-1 K-1, T is the standard temperature of 298 K and K'eq = [products]/[reactants].For a biochemical reaction,if the free energy change is negative, the reaction is said to be spontaneous or exergonic. Such reactions do not require the input of energy.If the free energy change is positive, the reaction is said to be non-spontaneous or endergonic. such a reaction would require an input of energy to occur.The standard free energy change of a chemical reaction is an alternative way of expressing its equilibrium constant. if K'eq=1, then reactant concentration = product concentration, ΔG'° will be zero.if K'eq>1, there is less reactant and more product, and ΔG'° will be negative.if K'eq<1, there is more reactant and less product, ΔG'° will be positive. A positive ΔG'° doesn't imply that a given reaction cannot proceed in the forward direction. A positive ΔG'° simply means that at equilibrium, there is more reactant in the solution than product. A reaction with ΔG'° = +ve can be driven forward if the product concentration is sufficiently low. Such is the case of oxidation of malate by NAD. Cellular processes continuously remove oxaloacetate from the solution such that it is present in nanomolar concentration. So, despite of a +ΔG'°, the reaction is driven forward.Since only the second statement fits with the reasoning above, it is the correct choice. The first statement is incorrect because endergonic reactions are non-spontaneous and the statement claims otherwise. The third statement is incorrect because it assumes that the oxidation of fumarate is coupled with the oxidation of malate. In coupled reactions, the energy released from energetically favourable reactions drives the energetically unfavourable reaction forward. The fourth statement is incorrect because malate oxidation requires NAD as an electron acceptor. NADH is a byproduct of the reaction, not one of the co-reactants and reduction of NAD to NADH does not release energy. As per the question, biochemical standard free energy for the reaction = +29 kJ/molpH = 7 or [H+} = 107 M[NADH]/[NAD] = 1/8The temperature is 25 + 273 = 298 KR is the universal gas constant equal to 8.314 J mol-1 K-1We substitute these values in the free energy change equation to determine the value of Keq:ΔG'° = R. T. In KeqIn Keq = ΔG'°/R.TIn Keq = (29 kJ/mol) / (8.314 J/mol.K × 298K)In Keq = 11.7050Keq = antilog 11.7050 Keq = 121,177.0487We know that Keq = [oxaloacetate] [NADH] [H+] / [malate] [NAD+] and Keq = 121177, so: [oxaloacetate] [NADH] [H+] / [malate] [NAD+] = 121,177{[oxaloacetate] × 1 × 107 } / {[malate] × 8} =121,177[oxaloacetate] / [malate] = (121,177 × 8) / 107[oxaloacetate] / [malate] = 0.0969[malate] / [oxaloacetate] = 1/0.0969[malate] / [oxaloacetate] = 10.3199The correct choice is the second statement: malate to oxaloacetate ratio is 10.3199