Why do we taste?

Why do we taste?

• Evaluate nutritious content of food

• Prevent the ingestion of toxic substances

Why do we taste?

What can we taste?

What can we taste?

Mammals are believed to distinguish only five basic tastes:

What can we taste?

Mammals are believed to distinguish only five basic tastes:

Sweet, sour, bitter, salty and umami (msg)Umami: Japanese for “delicious flavor”

Sweet:

Umami:

Salt:

Sour and bitter:

Sweet: Identify energy-rich nutrients

Umami

Salt:

Sour and bitter:

Sweet: Identify energy-rich nutrients

Umami: Recognize amino acids

Salt:

Sour and bitter:

Sweet: Identify energy-rich nutrients

Umami: Recognize amino acids

Salt: Ensures proper dietary electrolyte balance

Sour and bitter:

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

Taste test: Phenylthiocarbamide (PTC)

Arthur Fox, "The Relationship Between Chemical Constitution and Taste” (Arthur Fox and C.R. Noller)

Albert Blakeslee, "Genetics of Sensory Thresholds: Taste for Phenyl Thio Carbamide"

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Taste test: Phenylthiocarbamide (PTC)

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Phenotype:

Strong taster __________Weak taster __________Non-taster __________

Phenotype:

Strong taster __________Weak taster __________Non-taster __________

Tasters: 70%Nontasters: 30%

Why do we taste?

What can we taste?

How can we taste?

There are variations in sensitivity to the basic tastes around the tongue.

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Chandrashekar et al. The Receptors and Cells for Mammalian Taste. Nature. (444) p. 288. 2006.

Chandrashekar et al. The Receptors and Cells for Mammalian Taste. Nature. (444) p. 288. 2006.

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Miracle Fruit - Synsepalum dulcificumMakes everything taste sweet

Miraculin - a glycoprotein found in Miracle Fruit can possibly change the structure of taste cell receptors

Sweet receptors are activated by acid

Bitter taste receptors:

- Scientists have identified 30 bitter taste receptors

- PTC taste receptor identified in 2003

- Chromosome 7: Single exon - 1002 base pairs

Kim, U-K et al. “Positional Cloning of the Human Quantitative Trait Locus Underlying Sensitivity to Phenylthiocarbamide” Science 299 (1221 - 1225). 2003.

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PTC taste receptor structure

Seven-transmembrane domain G-protein coupled receptor.

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Binding of PTC leads to release of intracellular calcium

SNPs - Single Nucleotide Polymorphisms

Sequencing revealed 3 nucleotide positions that varywithin the human population:

Nucleotide TasterCodon AA

145 CCA P785 GCT A886 GTC V

SNPs - Single Nucleotide Polymorphisms

Sequencing revealed 3 nucleotide positions that varywithin the human population:

Nucleotide Taster NontasterCodon AA Codon AA

145 CCA P GCA A785 GCT A GTT V886 GTC V ATC I

SNPs - Single Nucleotide Polymorphisms

Sequencing revealed 3 nucleotide positions that varywithin the human population:

Nucleotide Taster NontasterCodon AA Codon AA

145 CCA P GCA A785 GCT A GTT V886 GTC V ATC I

A combination of SNPs = haplotype

SNPs - Single Nucleotide Polymorphisms

Sequencing revealed 3 nucleotide positions that varywithin the human population:

Nucleotide Taster NontasterCodon AA Codon AA

145 CCA P GCA A785 GCT A GTT V886 GTC V ATC I

A combination of SNPs = haplotype

Question:

Does your genotype for the PTC receptor correlatewith phenotype?

Question:

Does your genotype for the PTC receptor correlatewith phenotype?

How do we study genotype?What material do we need to start with?

PTC Lab Protocol

DAY 1: DNA isolation

Waivers / Assign numbers

http://www.dnai.org/b/index.html

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