2PTC and the Ability to Taste PhenylthiocarbamideThe TAS2R38 gene is determinant of one's ability to taste bitter, which is found in many common foods and drinks like coffee, beer, and bitter tasting vegetables.
3Significance of PTCThe chemical structure of PTC is similar to that of thiocyanates that are found in broccoli, cauliflower, brussel sprouts.Genetic variation the three predominant alleles for PTC tasting are PAV, AVI, and AAV.All three alleles are found in the European population, while AAV is common in Asia and PAV is found almost exclusively in native Americans.
4PTC GenesThere are two common forms (or alleles) of the PTC gene, and at least five rare forms. One of the common forms is a tasting allele(PAV), and the other is a non-tasting allele(AVI). Each allele codes for a bitter taste receptor protein with a slightly different shape. The shape of the receptor protein determines how strongly it can bind to PTC. Since all people have two copies of every gene, combinations of the bitter taste gene variants determine whether someone finds PTC intensely bitter, somewhat bitter, or without taste at all.
5Why is this a BIG Deal?Well it turns out it is a really small deal. The difference between a taster and a nontaster is in the 961 base pair sequence of the PTC gene at position 782 “c becomes t” and amino acid alanine becomes valine AND at position 886 “g becomes a” and amino acid 296 changes from valine to isoleucine.
7Catherine DeMedici Could You BE a Victim? Although PTC is not found in nature, the ability to taste it correlates strongly with the ability to taste other bitter substances that do occur naturally, many of which are toxins.
8Directions for LabObtain one piece each of PTC paper and untreated taste paper from your instructor. Place the untreated paper on your wet tongue to see how it tastes. Dispose of this piece of paper in the trash can. Next, place the PTC paper on your wet tongue to see if you can taste the chemical. Discard the PTC paper in the trash can.
9Ability to Taste PTCThe first phenotype you will determine is whether or not you can taste a chemical called PTC (phenylthiocarbamide) or not. The chemical is harmless, but produces a very bitter taste for those who are able to taste it. The trait for being able to taste this chemical is dominant and the corresponding gene is represented by the capital letter “T.”If you are unable to taste then you will represent your phenotype by “t”
10The Ability to Taste Thiourea The first phenotype you will determine is whether or not you can taste a chemical called Thiourea. For this gene if you are able to taste the strip you will be a “B”If you are unable to taste the strip then you will be a “b”
11The Ability to Taste Sodium Benzoate The first phenotype you will determine is whether or not you can taste a chemical called Sodium benzoate. For this gene if you are able to taste the strip you will be a “D”If you are unable to taste the strip then you will be a “d”