An enzyme is a globular protein that speeds a reaction up without being used up. It works by making the hardest step easier — and everything about its shape, its collisions and its inhibitors comes back to that one idea.
Enzymes are biological catalysts — globular proteins that speed up the chemical reactions of metabolism. Like all catalysts they are not consumed, so a single enzyme molecule works over and over.
They lower the activation energy: the energy barrier a reaction must cross before it can proceed. A lower barrier means far more reactant molecules have enough energy to react, so the reaction goes faster.
The substrate binds at a specific region called the active site. Only a substrate with a complementary shape fits, which is why each enzyme catalyses only its own reaction — its specificity.
The active site isn't a rigid mould. When the substrate binds, both it and the enzyme change shape — and that reshaping is what strains the substrate's bonds and drives the reaction. Step through it, or press Play.
Nothing happens until a substrate physically collides with the active site — moving randomly in Brownian motion, it must hit with enough energy and the correct orientation. Raising the temperature or the concentration makes those successful collisions more frequent.
Because catalysis depends on a precisely shaped active site, anything that changes that shape changes what the enzyme can do — or destroys it entirely.
No energy transfer is ever 100% efficient, so every metabolic reaction loses some energy as heat. In respiration, only around 40% of the energy in glucose is captured in ATP — the rest is released as heat. It is unavoidable.
Endotherms — mammals and birds — use this heat to hold a body temperature above their surroundings. What would otherwise be waste becomes the basis of temperature homeostasis.
Metabolism is organised into pathways — sequences of enzyme-controlled steps. Tap each type.
Breaking one overall change into many small enzyme-controlled steps gives far more points of regulatory control. Each intermediate is a place the cell can speed up, slow down, or switch the whole pathway off.
Inhibitors slow enzymes down — and where they bind decides whether more substrate can overcome them. Tap each mechanism.
A competitive inhibitor blocks the active site itself, so adding more substrate can out-compete it. A non-competitive inhibitor binds an allosteric site elsewhere, changing the active site's shape — extra substrate cannot reverse that.
Plot rate against substrate concentration and the two mechanisms separate cleanly. Toggle each inhibitor and watch the curve move — the whole distinction is whether Vmax can still be reached.
The standard curve: rate climbs steeply, then levels off at Vmax once every active site is working flat out and the enzyme is saturated. The dashed line marks that ceiling — compare where each inhibitor leaves it.
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Everything about an enzyme flows from one shaped pocket. The active site lowers activation energy by induced fit, its specificity controls which reaction happens, and denaturation or inhibitors work by disrupting that same shape.
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Drag each term into the gap it belongs in. Two terms are traps.
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