What is Enzyme? Explain their nomenclature and classification.

What is an Enzyme?

An enzyme is a biological catalyst that speeds up chemical reactions in living organisms without being consumed in the process. Enzymes are typically proteins, although some RNA molecules (ribozymes) also exhibit catalytic activity. Enzymes play a crucial role in various physiological processes, including digestion, metabolism, DNA replication, and energy production. They work by lowering the activation energy required for a reaction to occur, thereby increasing the rate of the reaction. Each enzyme is specific to a particular substrate, often reflecting the "lock and key" model, where the enzyme's active site fits precisely with the substrate.

Nomenclature of Enzymes

Enzyme nomenclature is based on a systematic system developed by the International Union of Biochemistry and Molecular Biology (IUBMB). Enzymes are named based on the type of reaction they catalyze and often include the substrate they act upon. The general naming convention follows these rules:

1. Prefix or Suffix: Enzyme names usually end in “-ase.” For example, lipase (for the breakdown of lipids) and amylase (for the breakdown of starch).
2. Substrate or Reaction Type: The name often reflects the substrate the enzyme acts on or the type of reaction it catalyzes. For example, lactase breaks down lactose, while protease breaks down proteins.
3. EC Number: Enzymes are also assigned a unique Enzyme Commission (EC) number, a four-part code that classifies them based on the reaction type they catalyze.

Classification of Enzymes

Enzymes are classified into six main categories, based on the type of reaction they catalyze:

1. Oxidoreductases: These enzymes catalyze oxidation-reduction reactions, where electrons are transferred between molecules. Example: Dehydrogenases (e.g., lactate dehydrogenase).
2. Transferases: These enzymes transfer functional groups (such as methyl, acetyl, or phosphate groups) from one molecule to another. Example: Kinases (e.g., hexokinase).
3. Hydrolases: These enzymes catalyze hydrolysis reactions, breaking bonds using water. Example: Lipase (breaks down lipids).
4. Lyases: These enzymes catalyze the breaking of bonds without using water or oxidation, often forming new double bonds or rings. Example: Decarboxylases (e.g., pyruvate decarboxylase).
5. Isomerases: These enzymes catalyze the rearrangement of atoms within a molecule, converting it into its isomer. Example: Phosphoglucose isomerase.
6. Ligases: These enzymes catalyze the joining of two molecules, typically requiring ATP or another high-energy molecule. Example: DNA ligase.

Enzyme classification allows for an organized approach to studying enzymes, helping to identify their roles in metabolism and other biochemical pathways.

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