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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" Taste test: Phenylthiocarbamide (PTC) Qu i c k T i m e ™ a n d a T I F F (L Z W ) d e c o m p re s s o r a re n e e d e d to s e e th i s p i c t u re . Qu i c k T i m e ™ a n d a T I F F (L Z W ) d e c o m p re s s o r a re n e e d e d to s e e th i s p i c t u re . 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. QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. Chandrashekar et al. The Receptors and Cells for Mammalian Taste. Nature. (444) p. 288. 2006. QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. Chandrashekar et al. The Receptors and Cells for Mammalian Taste. Nature. (444) p. 288. 2006. Miracle Fruit - Synsepalum dulcificum Makes 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. PTC taste receptor structure QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. Seven-transmembrane domain G-protein coupled receptor. QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. Binding of PTC leads to release of intracellular calcium SNPs - Single Nucleotide Polymorphisms Sequencing revealed 3 nucleotide positions that vary within the human population: Nucleotide 145 785 886 Taster Codon AA CCA GCT GTC P A V SNPs - Single Nucleotide Polymorphisms Sequencing revealed 3 nucleotide positions that vary within the human population: Nucleotide 145 785 886 Taster Codon CCA GCT GTC AA Nontaster Codon AA P A V GCA GTT ATC A V I SNPs - Single Nucleotide Polymorphisms Sequencing revealed 3 nucleotide positions that vary within the human population: Nucleotide 145 785 886 Taster Codon CCA GCT GTC AA Nontaster Codon AA P A V GCA GTT ATC A V I A combination of SNPs = haplotype SNPs - Single Nucleotide Polymorphisms Sequencing revealed 3 nucleotide positions that vary within the human population: Nucleotide 145 785 886 Taster Codon CCA GCT GTC AA Nontaster Codon AA P A V GCA GTT ATC A V I A combination of SNPs = haplotype Question: Does your genotype for the PTC receptor correlate with phenotype? Question: Does your genotype for the PTC receptor correlate with 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 Amazon - Dancing Naked in the Mind Field