Enzymes are specialized proteins that act as biological catalysts, accelerating chemical reactions within living organisms. They play a fundamental role in almost all biochemical processes, allowing cells to carry out necessary metabolic reactions efficiently. Enzymes exhibit specific characteristics and are classified based on their structure, function, and mode of action.

General Characteristics of Enzymes

Protein Nature: Enzymes are predominantly composed of proteins, although some RNA molecules called ribozymes also exhibit catalytic activity. Proteins are made up of amino acids linked together by peptide bonds, and the unique sequence and arrangement of amino acids in an enzyme determine its structure and function.

Specificity: Enzymes display high specificity for their substrate(s), the molecule(s) on which they act. Each enzyme recognizes and binds to a particular substrate(s) due to complementary molecular interactions, such as hydrogen bonding, electrostatic interactions, and hydrophobic interactions. This specificity allows enzymes to catalyze specific reactions within a complex mixture of molecules.

Catalytic Activity: Enzymes increase the rate of chemical reactions by lowering the activation energy required for the reaction to occur. They achieve this by providing an alternative reaction pathway with a lower energy barrier, allowing the reaction to proceed more readily. Enzymes do not alter the overall energy change or equilibrium of a reaction; instead, they accelerate the attainment of equilibrium.

Efficiency: Enzymes are highly efficient catalysts, often increasing reaction rates by several orders of magnitude. This efficiency enables biochemical reactions to occur at a suitable rate under physiological conditions, ensuring the proper functioning of cells and organisms.

Regulation: Enzyme activity can be regulated to maintain optimal cellular function. Regulation occurs through various mechanisms, including allosteric regulation, covalent modification (e.g., phosphorylation), feedback inhibition, and gene expression control. Regulation allows cells to adjust enzyme activity in response to changing environmental conditions and metabolic requirements.

Reusability: Enzymes are not consumed during catalysis. Once a reaction is complete, enzymes can be reused to catalyze subsequent reactions. This property contributes to the overall efficiency and economy of biochemical processes.

Classification of Enzymes

Enzymes can be classified based on several criteria, including their structure, function, and mode of action. Here are some common methods of enzyme classification:

Classification based on Enzyme Commission (EC) Number: The EC number system is widely used for enzyme classification and is based on the type of reaction catalyzed. It consists of a four-digit number that represents specific enzyme classes, subclasses, sub-subclasses, and individual enzymes within sub-subclasses. For example, EC represents alcohol dehydrogenase, an enzyme that catalyzes the oxidation of alcohols.

Classification based on Reaction Type

a) Oxidoreductases: Catalyze oxidation-reduction reactions, transferring electrons from one molecule to another.

b) Transferases: Catalyze the transfer of functional groups (e.g., methyl, phosphate) between molecules.

c) Hydrolases: Catalyze the hydrolysis of bonds, breaking molecules into smaller units through the addition of water.

d) Lyases: Catalyze the addition or removal of groups from double bonds or the cleavage of bonds without the addition of water.

e) Isomerases: Catalyze the rearrangement of atoms within a molecule, forming isomers.