A coenzyme is an organic molecule required for the proper function of an enzyme, typically derived from vitamins, and is not consumed in the reaction it catalyzes. Option d is the correct option.
A coenzyme is a small organic molecule, often derived from dietary vitamins, that is required to enhance an enzyme's activity. Unlike a waste product or a temporary modification, coenzymes participate in enzymatic reactions by aiding in the transformation of substrates into products. These organic helper molecules, such as Vitamin C in collagen synthesis, are crucial for various biochemical reactions but are not permanently altered themselves - they are reusable.
Particularly, NADH and ATP are common examples of coenzymes supplying high-energy electrons and phosphate groups, respectively. In the absence of the necessary coenzyme, an enzyme is referred to as an apoenzyme and is inactive; conversely, with the coenzyme, it becomes a holoenzyme, thus active. Option d is the correct option.