Fill in the missing words in the following paragraph. Light is absorbed by the protein ______, which changes from _____ to a _____ configuration. This causes a structural change in the ____ protein. This conformational change allows the G protein called __________ to bind, and results in the exchange of _____ for GDP. The _______subunit of the G protein then activates the protein ______, which breaks down cGMP. The reduction in cGMP causes CNG channels to ______ and the cell to ______.