What best describes the action of a coenzyme?

Coenzymes are small organic molecules that play a crucial role in enzyme function by participating directly in the catalytic action of enzymes. They are often derived from vitamins and are not permanently bound to the enzyme, meaning they can associate with and dissociate from the enzyme in a dynamic process. During reactions, coenzymes assist enzymes by either donating or accepting specific atoms or chemical groups, facilitating the transformation of substrates into products. This participation is essential because many enzymes require coenzymes to function optimally, as they help to stabilize reactive intermediates or transport necessary chemical groups to or from the enzyme's active site. Thus, the defining characteristic of coenzymes is their active involvement in the reaction process, which distinguishes them from factors that might only enhance the enzyme's activity or stability without direct engagement in the reaction itself.