Nucleoside diphosphate (NDP) is a molecule composed of a nucleoside linked to two phosphate groups. It plays a crucial role in cellular metabolism and energy transfer. NDPs are involved in the synthesis of nucleotides, which are the building blocks of nucleic acids like DNA and RNA. In the body, NDPs can be converted into nucleoside triphosphates (NTPs) by the addition of an extra phosphate group. NTPs, such as ATP (adenosine triphosphate), are essential for various biochemical processes, including energy storage and transfer, signaling, and the synthesis of macromolecules.