Guanosine diphosphate (GDP) is a nucleotide that plays a crucial role in cellular energy transfer. It consists of a guanine base, a ribose sugar, and two phosphate groups. GDP is involved in various biochemical processes, including the conversion of energy in cells and the regulation of certain proteins. When a cell requires energy, GDP can be converted to guanosine triphosphate (GTP) through the addition of a phosphate group. This conversion is essential for processes such as protein synthesis and signal transduction, making GDP an important molecule in cellular metabolism and function.