Enzymes are macromolecules that act as catalysts to speed up chemical reactions in living organisms by lowering their activation energy. They have extraordinary specificity and catalytic power, breaking down foods and converting molecules like glucose and fructose to form sucrose. Enzymes help with processes like digestion by converting substrates into specific products through a "lock and key" fit between the enzyme's active site and the substrate's shape. Inhibition can slow or stop enzymes, with competitive inhibitors resembling substrates and non-competitive inhibitors binding elsewhere on the enzyme.