A catalyst is a substance that increases the rate of a chemical reaction without being used up. Enzymes are biological catalysts.For any reaction to happen, the reacting molecules need a minimum amount of energy, the activation energy. Enzymes work by lowering the activation energy. This means many more molecules have enough energy to react, so reactions happen quickly at body temperature (about 37 °C in humans), which is far too low for most of them to happen at a useful rate otherwise.
• when two substrate molecules must join, the active site holds them close together in the right orientation
• when a substrate is broken down, binding puts strain on its bonds, so they break more easilyEnzymes do not change the products of a reaction or the overall energy change; they only make the reaction faster.Because an enzyme is unchanged at the end of each reaction, it can be used again and again. So enzymes are needed only in small amounts. The number of substrate molecules one enzyme molecule converts per second is its turnover number; for many enzymes this is thousands per second.Worked example: an enzyme molecule converts 500 substrate molecules per second. In 10 s it converts 500 × 10 = 5000 molecules; in 2 minutes (120 s) it converts 500 × 120 = 60 000 molecules.
• when two substrate molecules must join, the active site holds them close together in the right orientation
• when a substrate is broken down, binding puts strain on its bonds, so they break more easilyEnzymes do not change the products of a reaction or the overall energy change; they only make the reaction faster.Because an enzyme is unchanged at the end of each reaction, it can be used again and again. So enzymes are needed only in small amounts. The number of substrate molecules one enzyme molecule converts per second is its turnover number; for many enzymes this is thousands per second.Worked example: an enzyme molecule converts 500 substrate molecules per second. In 10 s it converts 500 × 10 = 5000 molecules; in 2 minutes (120 s) it converts 500 × 120 = 60 000 molecules.