Coenzymes are small organic molecules that assist enzymes in catalyzing biochemical reactions. They often act as carriers for chemical groups or electrons, helping to facilitate the transformation of substrates into products. Common examples of coenzymes include NAD+, FAD, and coenzyme A, which play crucial roles in metabolic pathways. These molecules are typically derived from vitamins, meaning that a deficiency in certain vitamins can lead to a lack of necessary coenzymes. Without adequate coenzymes, enzymes may not function effectively, disrupting essential biological processes such as cellular respiration and fatty acid synthesis.