The function of coenzymes in metabolism is to assist enzymes in catalyzing biochemical reactions. Coenzymes, often derived from vitamins, play an essential role in metabolic pathways by helping the enzymes work more efficiently. They participate in various processes, like the conversion of substrates into energy and the synthesis of macromolecules. Without coenzymes, many enzymatic reactions would not occur at an adequate rate, hindering cellular function and overall metabolism.