PTC - Can you taste bitter?

Internet Link – ScienceNow Picky Eaters Video

V: Drive Link – ScienceNow Picky Eaters Video

PCR Lab – PTC TasterPCR Lab – PTC Taster

What DNA sequence What DNA sequence are we going to copy?are we going to copy?

TAS2R geneTAS2R gene

Encodes a PTC taste Encodes a PTC taste receptor (senses a receptor (senses a bitter taste)bitter taste)

Genetics Science Learning Center

The Anatomy of Taste

PCR Lab – PTC TasterPCR Lab – PTC Taster

What do we do with bitter taste receptors?What do we do with bitter taste receptors?

Many toxic plants are bitter tastingMany toxic plants are bitter tasting

People with high levels of bitter taste People with high levels of bitter taste receptors are less likely to smoke.receptors are less likely to smoke.

PCR Lab – PTC TasterPCR Lab – PTC Taster

Chance discoveryChance discovery

Background on TAS2R38 Gene (Bitter Taste):

• 1930’s -- 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

DNA…

TAS2R38: Chromosome 7

1002 bp long

…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)

Protein picture…

Cytoplasmic

PCR Lab – PTC TasterPCR Lab – PTC Taster

Being a “taster” is a dominant traitBeing a “taster” is a dominant trait

Homozygous dominant – TTHomozygous dominant – TT

Heterozygous – TtHeterozygous – Tt

Homozygous recessive - ttHomozygous recessive - tt

TASTERS

NON-TASTERS

PCR Lab – PTC TasterPCR Lab – PTC TasterNon-taster PCR Non-taster PCR product - product -

SNP – Single SNP – Single Nucleotide Nucleotide Polymorphism. Polymorphism. One “letter” One “letter” makes a big makes a big difference.difference.

Taster PCR Taster PCR product - product -

221 bp221 bp

221 bp221 bp

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)