580.221_ Exam 3_2016 Name: ____________________________________ 20 F2. (4.5 points) Many people hate the taste of cilantro; a little over 12% of the population perceive it as tasting ‘soapy’ and this can ruin any meal that has cilantro in it. To the rest of the population, cilantro doesn’t have this soapy taste. A 2012 study in the journal Flavor identified a likely causative mutation for the soapy taste, a single nucleotide polymorphism in a region near the OR6A2 gene. OR6A2 is an olfactory receptor, “which has a high binding specificity for several of the aldehydes that give cilantro its characteristic odor”. As an olfactory receptor (OR), OR6A2 is a plasma membrane-bound GPCR.A. (1pt) If the mutation turns out to be in the extracellular domain of OR6A2, what is the likely functional change that results in the emergence of soapy flavor? B. (1pt) If the mutation turns out to be in the intracellular domain of OR6A2, what is the likely functional change that results in the emergence of soapy flavor? C. (1.5pt) Let’s say there is another receptor, OR6A3, that senses the aldehydes in actual soap, and therefore is the receptor through which we ‘taste’ soap if we (for whatever unfortunate reason) eat some soap. Unusually for ORs, the soap aldehydes only need to bind to OR6A3 to make us taste soap. Based on all the information provided in question F2 so far, do the aldehydes in cilantro activate OR6A3? Explain your reasoning. D. (1pt) I noted in part C that OR6A3 would be unusual if it was the only OR required to taste soap. In reality, for the over 400 functional ORs, typically many odorants bind each OR, and many ORs bind each odorant. With this seemingly messy arrangement (sometimes known as ‘broad tuning’), explain how humans identify and discriminate tastes?