Globular proteins

- Enzymes are globular proteins which have a specific tertiary structure that has a complementary shape to substrate - The lock and key model is used to describe enzyme action. For example the enzyme lactase has an active site (a lock) that is complementary only to lactose (the key). - Sucrose, a similar disaccharide has a different shape to lactose and so cannot bind to lactase’s active site. On binding to the active site, an enzyme-substrate complex is formed and reaction takes place. - The products have a different shape and can no longer remain bound. - In the induced fit model, the active site is not complementary to the substrate, but on binding the shape changes and the active site forms, molding itself to the substrate a tight glove would mould to a hand.