text: GTPases function as molecular switches or timers in many fundamental cellular processes.
  Examples of these roles include: 
  * Signal transduction in response to activation of cell surface receptors, including transmembrane receptors such as those mediating taste, smell and vision.
  * Protein biosynthesis (a.k.a. translation) at the ribosome. 
  * Regulation of cell differentiation, proliferation, division and movement. 
  * Translocation of proteins through membranes. 
  * Transport of vesicles within the cell, and vesicle-mediated secretion and uptake, through GTPase control of vesicle coat assembly.
  GTPases are active when bound to GTP and inactive when bound to GDP. In the generalized receptor-transducer-effector signaling model of Martin Rodbell, signaling GTPases act as transducers to regulate the activity of effector proteins. This inactive-active switch is due to conformational changes in the protein distinguishing these two forms, particularly of the "switch" regions that in the active state are able to make protein-protein contacts with partner proteins that alter the function of these effectors.