This statement about enzymes is true

The correct option is All of the above.

To understand why this is the correct choice, let us break down each of the statements individually:

1. Enzymes are proteins whose three-dimensional form is key to their function:
Enzymes are highly specific biological catalysts composed of amino acid chains folded into complex three-dimensional structures. This specific conformation creates an active site that uniquely fits particular substrate molecules (often explained by the lock-and-key model or induced-fit model). If this three-dimensional shape is disrupted or denatured by heat or pH changes, the enzyme loses its catalytic ability.

2. Enzymes accelerate reactions by lowering the activation energy:
For a chemical reaction to occur, reactant molecules must absorb a minimum amount of energy to reach an unstable transition state. This energy barrier is known as the activation energy. Enzymes speed up reactions by stabilizing this transition state, effectively lowering the activation energy barrier ($E_a$) so that more reactant molecules can successfully transition to products in a given timeframe.

3. Enzymes do not alter the overall change in free energy for a reaction:
The overall change in free energy ($\Delta G$) is a thermodynamic state function determined solely by the difference in free energy between the reactants and the products. Because enzymes only speed up the rate at which equilibrium is reached but do not change the initial or final energy states of the molecules involved, they have no effect on the value of $\Delta G$.

Since all three individual statements are correct, the correct choice is indeed All of the above.