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To Taste or Not to Taste?
PTC and the Ability to Taste
Phenylthiocarbamide
The 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.
Significance of PTC
• The 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.
PTC Genes
• There 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.
Why 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.
Catherine 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.
Directions for Lab
• Obtain 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.
Ability to Taste PTC
• The 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”
The 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”
The 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”