Nucleoside diphosphates (NDPs) are organic molecules composed of a nucleoside linked to two phosphate groups. They play a crucial role in cellular metabolism and energy transfer. NDPs can be converted into nucleoside triphosphates (NTPs), which are essential for various biological processes, including DNA and RNA synthesis. Common examples of nucleoside diphosphates include ADP (adenosine diphosphate) and GDP (guanosine diphosphate). These molecules are involved in signaling pathways and energy production within cells. The conversion between NDPs and NTPs is vital for maintaining the energy balance in living organisms.