Guanosine triphosphate (GTP) is a nucleoside triphosphate that is similar in structure to ATP and is an energy-rich molecule. It is composed of a ribonucleoside and three phosphate groups, with a guanine base bound to the 1 carbon of the ribose sugar and the triphosphate moiety attached to the riboses 5 carbon. GTP is used as a source of energy for protein synthesis and gluconeogenesis, and it is involved in energy transfer within the cell. It is also used as an energy source for the binding of a new amino-bound tRNA to the A site of the ribosome during the elongation stage of translation, and for the translocation of the ribosome towards the 3 end of the mRNA. GTP is essential to signal transduction, in particular with G-proteins, in second-messenger mechanisms where it is converted to guanosine diphosphate (GDP) through the action of GTPases. GTP is also involved in microtubule dynamic instability and nuclear transport.