The mechanism of the activation of Smo by the hedgehog ligand binding to Ptch is not completely understood. However, the model shown in Figure 11.12 in the text shows a pathway with two membrane proteins, similar to the arrangement of membrane proteins in the hedgehog pathway. In this model, cellsignaling is involved when the ligand binds to the first receptor protein, activating the G protein. The G protein then activates the second membrane protein, which transduces the signal to the interior of thecell. Explain how this mechanism might be applied to the two membrane proteins in the hedgehog signaling pathway.