Gproteins and g-protein-linked receptors g proteins and g-protein-linked receptors are thought to have evolved very early, because of their similar structure and function in a wide variety of modern organisms. are found only in bacterial cells, embedded in the cell's plasma membrane only. are not widespread in nature and were unimportant in the evolution of eukaryotes. probably evolved from an adaptation of the citric acid cycle. are found only in animal cells, and only embedded in or located just beneath the cell's membrane.