Is the substrate level phosphorylation (of succinate) spontaneous under conditions that exist in the mitochondria?
To determine if substrate level phosphorylation of succinate is spontaneous under conditions that exist in the mitochondria, let's break down the question and explain the concepts involved.
Substrate-level phosphorylation is a metabolic process in which ATP is synthesized through the direct transfer of a phosphate group from a substrate molecule to ADP. In the case of succinate, this process occurs during the citric acid cycle (also known as the Krebs cycle) in the mitochondria.
The spontaneity of a reaction can be determined by considering the change in Gibbs free energy (∆G) during the process. If ∆G is negative, the reaction is spontaneous, while a positive ∆G indicates a non-spontaneous reaction.
In the mitochondria, the citric acid cycle takes place under physiological conditions, where pH, temperature, and concentrations of reactants and products are regulated. The substrate-level phosphorylation of succinate involves the conversion of succinate to fumarate, with the transfer of a phosphate group to ADP to produce ATP.
To determine if this reaction is spontaneous, we need to know the ∆G value. The ∆G of a reaction can be calculated using the equation:
∆G = ∆G° + RT ln(Q)
where ∆G° is the standard free energy change, R is the gas constant, T is the temperature in Kelvin, and Q is the reaction quotient.
In this case, we can use the ∆G° value (standard free energy change) for the reaction, which is -7.3 kcal/mol. The temperature, R, and the concentrations of reactants and products can be taken as physiological values.
By substituting these values into the equation and calculating ∆G, you can determine if the substrate level phosphorylation of succinate is spontaneous under conditions that exist in the mitochondria. If ∆G is negative, it is spontaneous, and if ∆G is positive, it is non-spontaneous.