Using what you have learned about changes in Gibbs free energy, would you predict the ∆G value of catabolic reactions to be positive or negative? What about anabolic reactions? Justify your answers using the terms 'enthalpy' and 'entropy.'

Verified step by step guidance

1. Understand the terms: Gibbs free energy (ΔG) is a measure of the spontaneity of a reaction. A negative ΔG indicates a spontaneous reaction, while a positive ΔG indicates a non-spontaneous reaction.
2. Define catabolic and anabolic reactions: Catabolic reactions break down molecules into smaller units, releasing energy. Anabolic reactions build larger molecules from smaller ones, consuming energy.
3. Relate ΔG to catabolic reactions: In catabolic reactions, the overall energy of the system decreases as complex molecules are broken down, which generally increases the entropy (disorder) of the system. This typically results in a negative ΔG, indicating spontaneity.
4. Relate ΔG to anabolic reactions: Anabolic reactions require energy to synthesize complex molecules from simpler ones, which decreases the entropy of the system. This typically results in a positive ΔG, indicating non-spontaneity.
5. Apply enthalpy and entropy: In catabolic reactions, the decrease in enthalpy (ΔH) and increase in entropy (ΔS) contribute to a negative ΔG. In anabolic reactions, the increase in enthalpy and decrease in entropy contribute to a positive ΔG.

Key Concepts

Gibbs Free Energy (∆G)

Gibbs free energy (∆G) is a thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure. A negative ∆G indicates that a reaction is spontaneous and can occur without external energy input, while a positive ∆G suggests that the reaction is non-spontaneous and requires energy input to proceed.

Catabolic and Anabolic Reactions

Catabolic reactions involve the breakdown of complex molecules into simpler ones, releasing energy in the process, which typically results in a negative ∆G. In contrast, anabolic reactions build complex molecules from simpler ones, requiring an input of energy, and are characterized by a positive ∆G. Understanding these processes is crucial for predicting the energy changes associated with metabolic pathways.

Enthalpy and Entropy

Enthalpy (H) refers to the total heat content of a system, while entropy (S) measures the degree of disorder or randomness in a system. The relationship between these two concepts is captured in the Gibbs free energy equation: ∆G = ∆H - T∆S. A reaction is favored when the change in enthalpy is negative (exothermic) and/or the change in entropy is positive (increased disorder), contributing to a negative ∆G for catabolic reactions and a positive ∆G for anabolic reactions.