PTC - Can you taste bitter?

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PTC - Can you taste bitter?
Internet Link ScienceNow Picky Eaters Video
V Drive Link ScienceNow Picky Eaters Video
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PCR Lab PTC Taster

• What DNA sequence are we going to copy?
• TAS2R gene
• Encodes a PTC taste receptor (senses a bitter
  taste)

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The Anatomy of Taste
Genetics Science Learning Center
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PCR Lab PTC Taster

• What do we do with bitter taste receptors?
• Many toxic plants are bitter tasting
• People with high levels of bitter taste receptors
  are less likely to smoke.

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PCR Lab PTC Taster

• Chance discovery

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Background on TAS2R38 Gene (Bitter Taste)

• 1930s -- first reported on variation of ability
  to taste PTC (phenylthiocarbimide)
• PTC bitter taste has been widely used in
  Mendelian genetics studies
• Bitter taste
• Controlled by group of bitter taste receptors
• Gene family TAS2R
• Bitter taste receptors are TRANSMEMBRANE
• 7 helical regions that wind through the cell
  membrane

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DNA
TAS2R38 Chromosome 7 1002 bp long
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to Protein

• Non-tasters differ from tasters at 3 locations in
  the TAS2R38 gene

Non-taster (t) (AVI) Taster (T) (PAV)
Amino acid 49 GCA (Alanine) CCA (Proline)
Amino acid 262 GTT (Valine) GCT (Alanine)
Amino acid 296 ATC (Isoleucine) GTC (Valine)
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Protein picture
Cytoplasmic
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PCR Lab PTC Taster

• Being a taster is a dominant trait
• Homozygous dominant TT
• Heterozygous Tt
• Homozygous recessive - tt

TASTERS
NON-TASTERS
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PCR Lab PTC Taster

• Non-taster PCR product -

221 bp

• Taster PCR product -

221 bp

• SNP Single Nucleotide Polymorphism. One
  letter makes a big difference.

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Determing PTC genotype

• Extract DNA from cheek cells
• Amplify TAS2R38 region (PTC) using PCR
• Digest PTC-PCR product with HaeIII
• PCR product is 221 bp
• Taste allele (T) one HaeIII site
• Sizes of 177 bp and 44 bp
• Non-taste allele (t) no HaeIII site
• Remains uncut - 221 bp
• Can you predict bands for these genotypes?
• TT (PTC strong taster)
• Tt (PTC weak taster)
• tt (PTC non-taster)