GTPases are a family of enzymes that play a crucial role in cellular signaling and regulation. They bind and hydrolyze guanosine triphosphate (GTP), which acts as an energy source and signaling molecule. GTPases are involved in various cellular processes, including cell growth, differentiation, and movement. These proteins can exist in an active or inactive state, depending on whether GTP or guanosine diphosphate (GDP) is bound. When GTP is bound, the GTPase is active and can interact with other proteins to transmit signals. Examples of GTPases include Ras, Rho, and Rab, each serving specific functions in the cell.