How and why do enzymes work?

Enzymes are biological catalysts. They increase the speed of a reaction, without being affected or altered themselves. Our bodies contain hundreds of enzymes, each catalysing a particular reaction (increasing the reaction's speed), by reducing the amount of energy required to activate the reacting molecules - the activation energy. Enzymes are very important, and if they were not present, life as we know it would be possible. The core temperature of a healthy human body is …

…by-product of metabolism. It is a powerful oxidising agent and will kill cells unless it is broken down rapidly. Catalase is extremely fast acting: it can break down 600,000 molecules of hydrogen peroxide per second. Like every other enzyme, catalase speeds up the reaction be lowering the required activation energy. If the hydrogen peroxide was not broken down quickly, (e.g. there was no catalyst) then the hydrogen peroxide would build up and eventually kill us.