What Are Enzymes and Their Functions?

Enzymes are proteins that serve as biological catalysts. They are not permanently altered or depleted by these activities, but cells use them to speed up chemical reactions. They are, therefore, used repeatedly.

Without enzymes, the cellular processes required for life would not move swiftly enough to keep the organism alive. A protein's ability to perform specific tasks depends on its three-dimensional structure. As proteins make up enzymes, anything that alters the structure of a protein will affect the efficiency of the enzyme's functions.

Enzymes are frequently created to work optimally in the typical conditions found inside the cell where they are used. Enzyme efficiency declines as conditions deviate from the norm.

Enzymes are proteins that are made up of several polypeptide chains, also called amino acids, that have undergone repetitive folding and coiling. They have three-dimensional structures made of linear chains of amino acids. The amino acid sequence of an enzyme determines its catalytic activity.

Only a small percentage of the enzyme’s structure, which is situated around the binding sites, is involved in catalysis. An enzyme’s active site is made up of the catalytic and binding sites, and they each have their specific locations.

Enzymes are responsible for:

• The action of kinases and phosphatases (frequently involved in signal transduction and cell regulation).
• The generation of hormones.
• The action of myosin, a muscle protein that hydrolyzes ATP to cause a muscular contraction, which causes movement.
• Transporting cargo around the cell as part of the cytoskeleton.
• Transportation and absorption of nutrients.
• Cell division and repair.
• Detoxification.
• Breaking down large molecules of proteins or starches into smaller ones (by digestive enzymes, such as amylases and proteases) so they can be adequately absorbed in the intestines.
• Respiration, digestion, and metabolism.

Based on the type of reaction they catalyze, the International Union of Biochemists separates enzymes into six categories, which include the following:

1. Oxidoreductases: An enzyme that catalyzes the transfer of electrons from one form of a molecule (electron donor) to another (electron acceptor) during oxidation and reduction processes. Consider the enzyme pyruvate dehydrogenase as an illustration. For oxidoreductase enzymes, NADP+ or NAD+ are usually used as cofactors.
2. Transferases: Facilitate the exchange of a chemical group (or functional group) from one compound, known as the donor, to another compound, known as the recipient (called the acceptor). For instance, an enzyme called a transaminase moves an amino group from one molecule to another.
3. Hydrolases: Hydrolytic enzymes that catalyze the hydrolysis of a bond by cleaving the link and hydrolyzing it with water molecules. For instance, pepsin dissolves the peptide bonds that hold proteins together.
4. Lyases: Enzymes that catalyze cellular processes by forming new double bonds or joining existing ones without using hydrolysis or oxidation. For instance, aldolase, an enzyme involved in glycolysis, catalyzes the conversion of fructose-1, 6-bisphosphate to glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.
5. Isomerases: A group of enzymes that alters the isomer state of a molecule. Isomerases aid in intramolecular rearrangements by forming and breaking bonds. For instance, during glycogenolysis, phosphoglucomutase catalyzes the conversion of glucose-1-phosphate to glucose-6-phosphate (the phosphate group is moved from one position to another in the same substance). To swiftly release energy, glucose is formed from glycogen.
6. Ligases: A catalytic enzyme that facilitates the ligation (or joining) of two large molecules by creating a new chemical bond between them. For instance, DNA ligase catalyzes the creation of a phosphodiester link between two pieces of DNA.