The enzyme lipase is an example of:

Question

Accepted Answer

The correct option is 2:
The enzyme Lipase is correctly classified as a **Hydrolase**. Enzymes are scientifically grouped into seven classes based on the type of chemical reaction they catalyze, a classification established by the International Union of Biochemistry and Molecular Biology (IUBMB). Hydrolases belong to the third class (EC 3). The defining characteristic of a hydrolase is its function: to catalyze the cleavage of a chemical bond by adding water (a process known as hydrolysis). Lipase, specifically, catalyzes the hydrolysis of lipids, which are typically triglycerides (fats), into simpler absorbable components—namely, fatty acids and glycerol. It accomplishes this by attacking the ester bonds that link the fatty acid chains to the glycerol backbone, inserting a molecule of water to break the bond. This digestive process is crucial for the absorption of dietary fats and fat-soluble vitamins, making the name "Hydrolase" an accurate reflection of its fundamental mechanism of action.

The incorrect option is 1:
Transferases are enzymes belonging to the second major class (EC 2), and their primary role is fundamentally different from that of lipases. A transferase catalyzes the movement of a functional group, such as an amino group, a methyl group, or a phosphate group, from one molecule (the donor) to another (the acceptor). For instance, transaminases move amino groups, and kinases move phosphate groups. Their mechanism involves group relocation rather than cleaving a molecule via the introduction of water. Since lipase's reaction is defined by the cleavage of a lipid's ester bond using water, it cannot be categorized as a transferase.

The incorrect option is 3:
Isomerases represent the fifth class of enzymes (EC 5), and their function is solely to catalyze the rearrangement of atoms within a single molecule. This process converts a molecule into one of its isomers—a compound with the same chemical formula but a different structural or spatial arrangement. They do not add water, nor do they break the molecule into two distinct products; they merely reconfigure the existing structure. A common example is the conversion of glucose-6-phosphate to fructose-6-phosphate, which is a structural rearrangement. Lipase’s function is a major catabolic breakdown involving water, which is a hydrolytic mechanism, not an isomerization.

The incorrect option is 4:
Oxidoreductases are classified as the first major enzyme class (EC 1). These enzymes are responsible for catalyzing oxidation-reduction (redox) reactions, which involve the transfer of electrons or hydrogen atoms from one molecule to another. In essence, they change the oxidation state of the substrates. Dehydrogenases and reductases are common examples of this class. The reaction catalyzed by lipase is not an oxidation or a reduction reaction; it does not involve the transfer of electrons or a change in the oxidation state of the lipid molecule. Therefore, categorizing lipase—an enzyme that cleaves bonds with water—as an oxidoreductase would be fundamentally incorrect based on biochemical reaction type.