Coenzymes are small organic molecules that assist enzymes in catalyzing biochemical reactions. They often act as carriers for chemical groups or electrons, helping to transfer these components between different molecules. Common examples of coenzymes include NAD+, FAD, and coenzyme A, which play crucial roles in metabolic processes. These molecules are not proteins themselves but are essential for the proper functioning of enzymes. Coenzymes can be derived from vitamins, meaning that a deficiency in certain vitamins can lead to a lack of necessary coenzymes, ultimately affecting various metabolic pathways in the body.