Coenzyme, in an enzymatic reaction usually functions to

There is a specific location on an enzyme which binds to substrates and helps turn them into products. This location, called the active site, is where coenzymes bind. There are several ways coenzymes assist in enzyme function, including changing their shape to activate, or turn on, enzymes, or aiding in chemical reactions by acting as carriers of energy or molecular groups. In order to occur, chemical reactions might require or release energy. Remember the First Law of Thermodynamics: energy can neither be created nor destroyed. So, for an enzyme to function, sometimes energy is needed. The cell likes to be efficient in its use of energy, therefore it tries to capture and reuse energy. One of the ways it does this is through coenzymes.