What are Coenzymes?
Coenzymes are small, organic molecules that bind to enzymes and are essential for their catalytic activity.
Derived from vitamins, they act as carriers for chemical groups or electrons in enzymatic reactions.
Structure and Examples
1) Nicotinamide Adenine Dinucleotide (NAD⁺)
Structure: Two nucleotides (adenine and nicotinamide) joined by phosphate groups.
Function: Electron carrier in redox reactions.
Example: NAD⁺ to NADH in cellular respiration.
2) Flavin Adenine Dinucleotide (FAD)
Structure: Riboflavin bound to an adenine nucleotide.
Function: Electron carrier.
Example: FAD to FADH₂ in the citric acid cycle.
3) Coenzyme A (CoA)
Structure: Pantothenic acid, cysteamine group, and adenine nucleotide.
Function: Transfers acyl groups.
Example: Acetyl-CoA in the citric acid cycle.
4) Thiamine Pyrophosphate (TPP)
Structure: Thiazole and pyrimidine rings with two phosphate groups.
Function: Decarboxylation of alpha-keto acids.
Example: Pyruvate to acetyl-CoA.
5) Pyridoxal Phosphate (PLP)
Structure: Aldehyde group, pyridine ring, and phosphate group.
Function: Amino acid metabolism.
Example: Aminotransferases in transamination reactions.
6) Biotin
Structure: Bicyclic molecule with ureido and tetrahydrothiophene rings.
Function: Carboxylation reactions.
Example: Acetyl-CoA carboxylase in fatty acid synthesis.
7) Tetrahydrofolate (THF)
Structure: Pteridine ring, para-aminobenzoic acid, and glutamic acid.
Function: Transfers one-carbon units.
Example: Nucleotide synthesis.
Biochemical Functions of Coenzymes
Electron Transfer: NAD⁺ and FAD in redox reactions (e.g., cellular respiration).
Group Transfer: CoA and TPP in metabolic pathways (e.g., citric acid cycle).
Carboxylation and Decarboxylation: Biotin and TPP in metabolism.
One-Carbon Transfer: THF in nucleotide synthesis.
Amino Acid Metabolism: PLP in transamination and other amino acid reactions.
Coenzymes ensure the proper functioning of metabolic pathways and cellular health by facilitating various biochemical processes.
