Coenzyme

Coenzymes are non-protein chemical compounds that bind to an enzyme and are essential for the enzyme's catalytic activity. These molecules are often derived from vitamins and other organic molecules required in small amounts by an organism. Coenzymes play a pivotal role in the biochemical transformations that occur in all living organisms.

Function

Coenzymes function mainly as intermediates in the transfer of chemical groups between enzymes. They may be considered "helper molecules" that assist in biochemical transformations. For example, many coenzymes carry acetyl groups, phosphate groups, or electrons. One of the most well-known coenzymes is nicotinamide adenine dinucleotide (NAD), which plays a critical role in oxidation-reduction reactions in cellular respiration.

Types of Coenzymes

Coenzymes can be broadly classified into two types based on their interaction with the enzyme:

• Cosubstrates - These are transiently bound to the enzyme and are released either in their modified or unmodified forms after the reaction occurs. Examples include NAD and adenosine triphosphate (ATP).
• Prosthetic groups - These are tightly or even covalently bound to their enzyme and remain attached throughout the reaction. An example is flavin mononucleotide (FMN) in the enzyme complex I of the electron transport chain.

Biosynthesis

The biosynthesis of coenzymes varies significantly depending on their nature and function. Many coenzymes are synthesized from vitamins, which are essential nutrients that an organism must obtain from its diet. For instance, NAD is synthesized from niacin (vitamin B3), while coenzyme A is made from pantothenic acid (vitamin B5).

Role in Metabolism

Coenzymes are indispensable to metabolism as they are involved in numerous metabolic pathways. Their roles include:

• Glycolysis
• Citric acid cycle
• Fatty acid metabolism
• Amino acid metabolism
• DNA replication and DNA repair

Clinical Significance

Deficiencies in the vitamins required for the synthesis of coenzymes can lead to metabolic disorders. For example, a deficiency in niacin leads to pellagra, a disease characterized by diarrhea, dermatitis, and dementia.

See also

• Enzyme
• Metabolism
• Vitamin
• Biochemistry