‹ Biology simulationsBiology · AS Level 9700 · 3 EnzymesSeven simulations covering Topic 3: how enzymes work (3.1) and the factors that affect their activity (3.2). Dock a substrate in a 3D active site, fire collisions over the activation-energy hill, watch molecules react, then push temperature, pH, concentrations and inhibitors and read Vmax and Km off the curves.
An enzyme is a globular protein with a small pocket, the active site, whose shape and chemistry are complementary to one substrate. Bring the substrate in and watch it bind, react and leave as products. Compare the rigid lock-and-key picture with induced fit, where the site closes around the substrate.
Every reaction has an energy barrier. Only collisions with at least that much energy react. An enzyme provides a different route with a lower barrier, so at the same temperature far more collisions succeed. The enzyme changes nothing about the start and end of the reaction, only the hill in between.
Watch substrate molecules collide with enzymes. Each successful collision forms an enzyme-substrate complex for a moment and releases product. The rate is highest at the start, when substrate is plentiful, and falls as it runs out. The initial rate is the gradient of the product-time graph at t = 0.
Warming a reaction gives the molecules more kinetic energy, so they collide more often and more of the collisions have enough energy: the rate roughly doubles for every 10 °C. Past the optimum the enzyme's hydrogen bonds break, the tertiary structure unravels, the active site loses its shape and the rate collapses. Denaturation is not reversible.
The R groups lining the active site carry charges that hold the substrate and take part in the reaction. Extra H+ or OH− ions change those charges, break ionic and hydrogen bonds and distort the site. Each enzyme has an optimum pH matched to where it works: pepsin in the stomach, trypsin in the small intestine.
More substrate means more collisions, until every active site is busy and the rate levels off at Vmax. Km is the substrate concentration that gives half of Vmax: a low Km means a high affinity. A competitive inhibitor competes for the active site and raises the apparent Km; a non-competitive inhibitor binds elsewhere, distorts the site and lowers Vmax.
Trap the enzyme in alginate beads and pour the substrate through a column. The product comes out enzyme-free, the beads can be used again and again, and the enzyme tolerates higher temperatures and a wider pH range because the gel holds its shape. Lactose-free milk is made this way with immobilised lactase.
Seven interactive 3D and 2D simulations for Cambridge AS Level Biology 9700 topic 3 Enzymes: the active site in 3D with lock-and-key and induced-fit binding, how an enzyme lowers the activation energy, the course of a reaction with colliding molecules and initial rate, the effects of temperature, pH, substrate and enzyme concentration with Vmax and Km, competitive and non-competitive inhibitors, and immobilised enzymes in alginate beads.
Seven simulations covering Topic 3: how enzymes work (3.1) and the factors that affect their activity (3.2). Dock a substrate in a 3D active site, fire collisions over the activation-energy hill, watch molecules react, then push temperature, pH, concentrations and inhibitors and read Vmax and Km off the curves.
Enzymes is a free, browser-based simulation for Cambridge International AS & A Level Biology 9700 (topic 3 Enzymes). The course is assessed in Paper 1 (Multiple choice), Paper 2 (AS structured), Paper 3 (Advanced practical), Paper 4 (A Level structured), Paper 5 (Planning, analysis, evaluation). Syllabus for examination in 2025-2027. There are 7 tabs, each a self-contained experiment with its own controls and live readings, and nothing to install: it runs on a laptop, tablet or classroom projector.
Full syllabus map: AS Level Biology 9700 topic 3.
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