Enzymes: mode of action

Every living cell runs thousands of chemical reactions every second, yet at body temperature almost all of them would be far too slow to keep you alive. Enzymes solve this. In this lesson we meet enzymes as globular proteins that act as biological catalysts, speeding metabolic reactions up while staying unchanged themselves. We see that some enzymes work inside the cell that made them (intracellular, like catalase) while others are secreted to work outside it (extracellular, like amylase and trypsin). We build the mode of action step by step — the active site, the enzyme-substrate complex, and the lowering of activation energy, which we draw as an energy pathway with and without an enzyme. We explain enzyme specificity through BOTH the lock-and-key hypothesis and the more modern induced-fit hypothesis. Finally we learn how to follow the progress of an enzyme-catalysed reaction — either by measuring the product formed, such as oxygen from catalase, or by measuring the substrate disappearing, such as starch broken down by amylase and tested with iodine.