Life depends on chemistry, but chemistry alone cannot sustain the complex processes of a living organism. Within every cell, thousands of chemical reactions must occur simultaneously and continuously to maintain existence. On the flip side, many of these reactions are thermodynamically unfavorable or proceed too slowly at the body’s typical temperature of around 37 degrees Celsius to be useful. Now, enzymes are biological catalysts—specialized proteins (and occasionally RNA molecules)—that accelerate chemical reactions without being consumed or permanently altered in the process. This is where enzyme-catalyzed reactions become indispensable. Without enzymes, the metabolic machinery of life would grind to a halt, making them the fundamental drivers of cellular function.
Not obvious, but once you see it — you'll see it everywhere.
What Are Enzymes and How Do They Work?
To understand which reactions require enzymes, one must first understand what enzymes are. Which means they function by lowering the activation energy required for a chemical reaction to proceed. Day to day, enzymes are highly specific biological catalysts. Activation energy is the initial input of energy needed to push reactants over an energy barrier; without an enzyme, this barrier is often insuratically high at physiological temperatures. By binding to the reactants, enzymes stabilize the transition state, effectively providing a lower-energy pathway for the reaction to occur Turns out it matters..
Adding to this, enzymes exhibit remarkable specificity. This specificity is often compared to a lock-and-key mechanism, where the enzyme's active site perfectly complements the shape of its substrate. Practically speaking, this means an enzyme typically catalyzes only one specific type of reaction or acts on a very narrow group of substrates. When the substrate binds, the enzyme induces a conformational change—often called the induced fit model—which further optimizes the interaction and positions the reactive groups for catalysis.
This is where a lot of people lose the thread.
Why Living Systems Cannot Rely on Non-Enzymatic Reactions
If enzymes are so crucial, why don't cells simply use non-enzymatic chemical catalysts, such as metal ions or simple inorganic catalysts, to drive these
