D-ribose (or ribose) is a simple 5-carbon sugar found in all living cells. It was thought to be primarily a structural component of DNA and RNA with little physiological significance. But a series of studies revealed that this sugar molecule played an intermediate role in an important metabolic reaction called the pentose phosphate pathway. This reaction is central to energy synthesis, the production of genetic material, and for providing substances used by certain tissues to make fatty acids and hormones.