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how do enzymes lower activation energy
One enzyme turns a reaction with a half-time of seventy-eight million years into one of eighteen milliseconds. Its trick is lowering the energy hill every reaction must climb.
The top of the hill is the transition state, a strained half-broken arrangement. The height from reactants to that peak is the activation energy.
With the enzyme, the reaction takes a lower path. The peak is lower, so far more molecules have enough energy to cross it every second.
Notice what did not move: same start, same end. The enzyme adds no energy and does not change the balance of reactants and products, only the speed.
How? The enzyme folds into a pocket called the active site, shaped to match the reaction's substrate and, even more, its transition state.
The substrate binds, and the enzyme squeezes and bends it toward the transition-state shape, gripping that shape most tightly. Stabilizing the peak is what lowers it.
Afterwards the products leave and the enzyme is back exactly as it was, ready to grab the next substrate. It is not used up.
That is why a little enzyme goes a long way: a single carbonic anhydrase molecule can handle about a million reactions every second.
So, the whole idea: the enzyme stabilizes the transition state, the hill drops, the reaction speeds up, and the start and end stay put.
Enzymes don't push reactions uphill; they carve a lower pass through the hill, again and again, without being used up.