Final answer:
G-proteins are an essential part of the cell signaling system, linking extracellular signals to intracellular responses by interacting with G-protein-linked receptors to control ion channels or enzymes.
Step-by-step explanation:
G-proteins are part of the cell signaling system and serve as a functional link between extracellular signals and intracellular responses. They act as molecular switches that are activated by G-protein-linked receptors. These receptors, which have seven transmembrane domains, bind to an external ligand, inducing a conformational change that activates the G-protein.
G-protein mediated signal transduction plays a crucial role in numerous physiological processes including vision, taste, and immune reactions, and when disrupted by bacterial toxins can result in serious illnesses such as pertussis, botulism, and cholera. For instance, in cholera, toxins produced by Vibrio cholerae alter a G-protein that controls a chloride channel, leading to severe dehydration.