Make your own free website on

Enzymes For Kids
Enzymes and health
Facts and Illustrations
Can we stop the reactions of enzymes?
Locks And Keys

What are ENZYMES???

The word enzyme comes from Greek: "in ferment". As early as the late 1700s and early 1800s the digestion of meat by stomach secretions and the conversion of starch to sugars by plant extracts and saliva were observed.

Studying the fermentation of sugar to alcohol by yeast, Louis Pasteur came to the conclusion that this fermentation was catalyzed by "ferments" in the yeast. In 1879, yeast extracts were used to ferment sugar independent from the living yeast cells by Eduard Buchner, proving that the fermentation was caused by molecules that functioned even outside the cells. He called these molecules enzymes.

An enzyme (in Greek en = in and zyme = blend) is a protein, or protein complex, that catalyses a chemical reaction and also controls the 3D orientation of the catalyzed substrates. Like any catalyst, enzymes work by lowering the activation energy of a reaction, thus allowing the reaction to proceed to its steady state or completion much faster than it otherwise would; the enzyme (again, as with any catalyst) remains unaltered by the completed reaction and can therefore continue catalysis. It is important to note that, as with all catalysts, all reactions catalyzed by enzymes must be 'spontaneous' i.e. with the enzyme, they run in the same direction as they would without the enzyme, just more quickly; the concept is similar to the likelihood of a ball rolling down a hill versus the likelihood of it rolling up the hill. Catalysis by an enzyme is analogous to removing a pebble that is stopping the ball from rolling down the hill; the reaction goes to completion more quickly, but the final product is identical. Given a particular starting set of conditions, the end products of a particular reaction (including net energy), once steady state is reached, must always be identical, independent of the specific individual pathway taken from beginning point to end point. This is required by the Law of Conservation of Energy, which would be violated by the possibility of a cycle of moving down a pathway releasing less net energy and back up a different pathway with higher net energy, or vice versa. An enzyme can, however, run a normally non-spontaneous reaction 'backwards by coupling it to a spontaneous one, as long as the net free energy from the total of both reactions is negative.

Enzymes are necessary within biological cells to control molecular shapes and because many chemical reactions would occur too slowly to sustain life; oxidation of organic food compounds to provide energy, for instance. Enzymes may speed up biochemical reactions by a factor of one thousand times or more. They also provide a means to control the reaction rates by modulating enzymatic activity


In a nutshell
Enzymes are catalysts. Most are proteins.

Enzymes bind temporarily to one or more of the reactants of the reaction they catalyze. In doing so, they lower the amount of activation energy needed and thus speed up the reaction.

Enter supporting content here