01Lowering activation energy
Every reaction needs an energy push to start: the activation energy (Eₐ). Enzymes lower Eₐ by orienting substrates, straining bonds, or providing a favorable microenvironment.
Enzymes do not change ΔG — the energy difference between reactants and products stays the same. They only change how fast equilibrium is reached.
02Reading the energy diagram
On an energy-vs-reaction-progress graph, the catalyzed curve has a lower hump, but starts and ends at the same heights as the uncatalyzed curve.
Exergonic reactions end lower than they start (release energy, ΔG < 0); endergonic reactions end higher (ΔG > 0).
03Notebook box
Enzyme changes: Eₐ ↓, rate ↑. Enzyme does NOT change: ΔG, equilibrium position, products.
Worked example: A graph shows two curves with the same start and end but different peaks. Which is enzyme-catalyzed and what is the same? → The lower peak; ΔG is identical.