Rat CA3 cells were infected to express a fusion protein consisting of YFP and one of these proteins in a 2005 paper by the Deisseroth group. The first chapter of William Bialek’s Biophysics describes how certain cells can act as perfect counters due to the femtosecond excited-state interconversion of these proteins. The duplication of LWS, one of these proteins, gave primates the ability to ascertain ripeness. The binding of arrestin-1 inhibits one of these proteins, which activates (*) transducin in a pathway in which a phosphodiesterase cleaves cGMP. Neurons expressing ChR2, (-5[1])one of these proteins, are selectively activated by lasers in a common optogenetic procedure. These GPCRs bind to the pigmented 11-cis-retinal, a Vitamin A-derived molecule that isomerizes after absorbing light. For 10 points, (-5[1])name these photoreceptors, one of which is encoded by the RHO gene. ■END■ (10[1])