The transaminase transfer of an amine group from alanine to α-ketoglutarate to form pyruvate and glutamate has a change in Gibb’s free energy (ΔG) of 1.9 kJ/mol. What does this ΔG value tell you about the reaction?

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The question provides a ΔG value of 1.9 kJ/mol for the transaminase reaction between alanine and α-ketoglutarate to form pyruvate and glutamate, and asks what this value implies about the reaction.
Option a: 'The reaction is non-spontaneous and requires input of energy.' A positive ΔG indicates non-spontaneity, but 1.9 kJ/mol is a relatively small positive value, not a large energy-demanding process. In biochemistry, such a tiny positive ΔG suggests the reaction is not strongly unfavorable, and is often reversible under cellular conditions rather than requiring substantial energy input.
Option b: 'The reaction is spontaneous and releases energy.' Spontaneity is associated with a negative ΔG (ΔG < 0). Since the given ΔG is +1.9 kJ/mol, this option is inconsistent with the thermodynamics; the reaction does not release energy and is not spontaneous under standard interpretation.
Option c: 'The reaction cannot occur under physiological conditions.' A small positive ΔG does not render a reaction impossible in the cell. Enzymes can drive such near-equilibrium reactions, and cellular conditions (concentrations, coupling with other processes) can permit the reaction to proceed in either direction. Therefore this claim is inaccurate.
Option d: 'The reaction is close to equilibrium and occurs in both directions.' A ΔG near zero, such as +1.9 kJ/mol, indicates the system is near equilibrium, with the reaction able to proceed reversibly in either direction depending on metabolite concentrations and cellular context. This aligns with the concept of transaminase reactions often being near equilibrium under physiological conditions.
Overall, the interpretation that fits the small, near-zero ΔG value is that the reaction sits close to equilibrium and can run in both directions, rather than being strongly spontaneous, energy-requiring, or physiologically blocked.

The transaminase transfer of an amine group from alanine to α-ketoglutarate to form pyruvate and glutamate has a change in Gibb’s free energy (ΔG) of 1.9 kJ/mol. What does this ΔG value tell you about the reaction?

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