Which functional property of enzymes allows them to be highly selective in chemical reactions?

The selectivity of enzymes in chemical reactions is primarily due to their specific shape. Enzymes are proteins that have a unique three-dimensional structure, which allows them to interact with specific substrates—the molecules upon which they act. The active site of an enzyme, where the substrate binds, is designed to fit particular substrate molecules, much like a lock and key mechanism. This specificity is essential for the enzyme’s function, as it ensures that the enzyme catalyzes only the intended reaction and does not interfere with other biochemical processes.

The other options do touch on characteristics of enzymes, but they do not directly contribute to their selectivity in the same way that their specific shape does. For instance, while enzymes do not change during reactions, this property pertains more to stability than selectivity. Requirement of high temperatures is not a universal characteristic of enzymes, as many function optimally at specific temperatures that are not necessarily high. Additionally, while some enzymes do function predominantly in one direction, many can catalyze reactions in both directions depending on the conditions, making this aspect less relevant to their selectivity.