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Bitter Taste: Taste Testing (Phenotype) and PCR (Genotype)

Bitter Taste: Taste Testing (Phenotype) and PCR (Genotype). Donna C. Sullivan, PhD Division of Infectious Diseases University of Mississippi Medical Center. Five Basic Tastes. Sweet Sour Bitter Salty Umami (the taste of monosodium glutamate). Why do we have these?.

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Bitter Taste: Taste Testing (Phenotype) and PCR (Genotype)

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  1. Bitter Taste: Taste Testing (Phenotype) and PCR (Genotype) Donna C. Sullivan, PhD Division of Infectious Diseases University of Mississippi Medical Center

  2. Five Basic Tastes • Sweet • Sour • Bitter • Salty • Umami (the taste of monosodium glutamate).

  3. Why do we have these? • Sweet: Identify energy-rich nutrients • Umami: Recognize amino acids • Salt: Ensures proper dietary electrolyte balance • Sour and bitter: Warn against the intake of potentially noxious or poisonous chemicals

  4. Phenylthiocarbamide (PTC) taste receptor • The inability to taste certain compounds is usually due to simple, recessive Mendelian inheritance. • Dozens of taste and odorant receptors have been cloned and sequenced in the last 20 years. • The TAS2R28 gene encodes a bitter taste receptor that enables humans to taste the compound PTC. • The PTC (TAS2R28) gene has a single coding exon, for a polypeptide chain with 333 amino acids.

  5. PTC taste receptor, continued • Three common single nucleotide polymorphisms (SNPs) are associated with PTC sensitivity. • Each SNP results in a change to the amino acid sequence of the PTC receptor.

  6. The Snps Are Usually Inherited Together In Certain Combinations, E.G., Haplotypes

  7. Certain Haplotypes Are Generally Correlated With Taster Status

  8. More Fun Informaton about PTC Receptor • PTC taste sensitivity displays a broad and continuous distribution (e.g., it behaves like a quantitative trait). • On average, PTC taste sensitivity is highest for the PAV/PAV (taster) homozygotes, slightly but significantly lower for the PAV heterozygotes, and lowest by far for the AVI/AVI (non-taster) homozygotes. • More rare AVI/AAV heterozygotes have a mean PTC score slightly, but significantly, higher than the AVI/AVI homozygotes. • All non-human primates examined to date are homozygous for the PAV (taster) haplotype. Thus, the AVI nontaster haplotype arose after humans diverged from the most recent common primate ancestor. • There are non-taster chimps: same gene, but different mutation than humans => molecular convergent evolution!!

  9. DNA Isolation

  10. PCR amplification

  11. Digest with HaeIII

  12. Gel electrophoresis

  13. Results • PCR amplification and restriction digestion identifies the G-C polymorphism in the TAS2R38 gene. • The “C” allele, on the right, is digested by HaeIII and correlates with PTC tasting.

  14. Results

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