Here's why:
* Enzyme Specificity: Enzymes are highly specific for their substrates. They have a unique active site that fits the shape and chemical properties of the specific molecule they are designed to break down.
* Sucrose Structure: Sucrose is a disaccharide made up of glucose and fructose linked by an α-1,β-2 glycosidic bond.
* Lactose Structure: Lactose is a disaccharide made up of glucose and galactose linked by a β-1,4 glycosidic bond.
The active site of sucrase is specifically designed to recognize and break the α-1,β-2 glycosidic bond in sucrose. It cannot recognize or hydrolyze the β-1,4 glycosidic bond in lactose.
In summary: Sucrase only breaks down sucrose because its active site is specifically shaped to bind and break the α-1,β-2 glycosidic bond, which is not present in lactose.
