Question

To what classes do the following enzymes belong? (a) Pyruvate decarboxylase (b) Chymotrypsin (c) Alcohol dehydrogenase

Short answer

(a) Lyases, (b) Hydrolases, (c) Oxidoreductases.

Step-by-step solution

Identify the enzyme classes

To determine the class to which each enzyme belongs, recall that enzymes are classified based on the general type of reaction they catalyze. There are six main classes.

Analyze enzyme name: Pyruvate decarboxylase

'Pyruvate decarboxylase' typically involves the removal of a carboxyl group from pyruvate, which is characteristic of the class of enzymes known as lyases. Lyases catalyze the breaking of various chemical bonds by means other than hydrolysis and oxidation, often forming a new double bond or a new ring structure.

Analyze enzyme name: Chymotrypsin

'Chymotrypsin' is a well-known protease, which means it catalyzes the cleavage of peptide bonds in proteins. Enzymes that hydrolyze peptide bonds are classified as hydrolases, which catalyze reactions that involve the cleavage of bonds by the addition of water.

Analyze enzyme name: Alcohol dehydrogenase

'Alcohol dehydrogenase' catalyzes the oxidation of alcohols, typically using NAD+ as a cofactor to accept electrons. This reaction type is characteristic of oxidoreductases, which catalyze oxidation-reduction reactions.

Key concepts

Decarboxylases

Decarboxylases are a unique group of enzymes that facilitate the removal of a carboxyl group from organic molecules. This reaction usually results in the production of carbon dioxide as a product.
In the case of pyruvate decarboxylase, it acts on pyruvate to release carbon dioxide, which is a crucial step in various metabolic pathways, such as fermentation.
- These enzymes play a significant role in the citric acid cycle and in the anaerobic pathway of alcoholic fermentation. - The main function of decarboxylases is the decarboxylation process, which leads to the breakdown of carboxylic acids. Decarboxylases are incredibly important for the energy production processes in cells by helping to channel carbon atoms from metabolites.

Proteases

Proteases are enzymes that are specialized in facilitating the breakdown of proteins. They achieve this by hydrolyzing peptide bonds within proteins and peptides. Chymotrypsin is a classic example of a protease.
Proteases fall under the hydrolase class because they catalyze reactions through the addition of water, effectively cleaving bonds: - These enzymes are crucial in many physiological processes, including digestion, immune response, and cell regulation. - By breaking down proteins into peptides and amino acids, proteases play a vital role in protein metabolism and recycling. Proteases are used in many industries, such as pharmaceuticals and food processing, due to their ability to specifically target peptide bonds.

Oxidoreductases

Oxidoreductases are enzymes that catalyze oxidation-reduction reactions, often involving the transfer of electrons between molecules.
Alcohol dehydrogenase is a prime example of an oxidoreductase, catalyzing the reversible oxidation of alcohols into aldehydes or ketones: - This enzyme uses cofactors, such as NAD+ or NADP+, to transfer electrons. - Alcohol dehydrogenase is important in the metabolism of alcohols within the body, performing crucial roles in processes like fermentation and respiration. These enzymes are fundamental to many biochemical processes, including cellular respiration where they facilitate the transfer of electrons in the electron transport chain, crucial for ATP production.

Hydrolases

Hydrolases are enzymes that break chemical bonds through the addition of water, a process commonly known as hydrolysis.
They cover a broad category of enzymes including proteases, esterases, and phosphatases: - Hydrolases are responsible for breaking down complex molecules into simpler ones, which can be further utilized by the body. - The digestive process heavily relies on hydrolases, such as amylase and lipase, to break down carbohydrates and fats. By catalyzing bond cleavage with water, hydrolases play essential roles in both catabolic and anabolic pathways, supporting functions ranging from nutrient digestion to DNA repair.

Lyases

Lyases are enzymes that catalyze the breaking of various chemical bonds through mechanisms other than hydrolysis and oxidation.
These reactions often result in the formation of a new double bond or a new ring without using high amounts of energy. - Lyases help in bonding or breaking down molecules, creating small molecules necessary for different metabolic pathways. - Unlike hydrolases, lyases do not incorporate water into the substrate when breaking bonds. These enzymes play a significant part in metabolic processes that include the synthesis and breakdown of amino acids and other key biological molecules, contributing to cellular structure and energy dynamics.