Uridine diphosphate, abbreviated UDP, is an organic compound.

It is an ester of pyrophosphoric acid with the nucleoside uridine.

UDP consists of the pyrophosphate group, the pentose sugar ribose, and the nucleobase uracil.

Before glucose can be stored as glycogen in the liver and muscles, the enzyme UDP-glucose pyrophosphorylase forms a UDP-glucose unit by combining glucose 1-phosphate with uridine triphosphate, cleaving a pyrophosphate ion in the process.

The UDP molecule is cleaved from the glucose ring during this process and can be reused by UDP-glucose pyrophosphorylase.