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)
QuickTi me™ and a
TIFF (LZW) decompressor
are needed to see this picture.
QuickTi me™ and a
TIFF (LZW) decompressor
are needed to see this picture.
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.
Quick Time™ 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