Bio Lab PTC UPDATED ACTUAL Exam
Questions and CORRECT Answers
objective - CORRECT ANSWER - characterize each student's ability to detect bitterness
using a PTC test strip; assess if response to unsweetened grapefruit juice correlates with PTC test
strip results; determine the density of taste bud-containing fungiform papillae (visual assay of the
anterior aspect of student's tongue; correlate with PTC test strip and grapefruit juice responses);
isolate DNA (saline mouth wash extraction), PCR amplify and (HaeIII restriction enzyme) digest
a short region of the TAS2R38 gene from each student to determine student genotype; Assess if
there is a relationship between genotype (TAS2R38 alleles) and phenotype (taste bud density,
response to PTC strip, grapefruit juice); examine the relationship between bitterness tasting
ability, avoidance of bitter tasting foods and incidence of cancer
five basic tastes - CORRECT ANSWER - sweet
sour
bitter
salty
umami (MSG L-form)
How does taste work? - CORRECT ANSWER - 1. taste molecule binds to receptor on
taste cell
2. cell generates a nervous impulse which is interpreted by the brain
*taste sensation is determined by wiring, not by which type of molecule is bound
phenylthiocarbamide (PTC) dust - CORRECT ANSWER - Arthur Fox tasted nothing, CR
Noller tasted bitterness
Albert Blakeslee - CORRECT ANSWER - inability to taste PTC is a recessive trait in
human populations (tasters 75%, nontasters 25%)
How many genes for bitter taste receptors? - CORRECT ANSWER - 30
, gene for PTC taste receptor - CORRECT ANSWER - TAS2R38; three SNPs correlate with
bitter tasting ability (five different haplotypes)
haplotype - CORRECT ANSWER - a specific combination of SNPs that correlates with a
trait
SNPs in serotonin transporter/receptor genes - CORRECT ANSWER - predict adverse
responses to anti-depression drugs (PROZAC/Paxil)
ability to taste PTC - CORRECT ANSWER - presence of at least one dominant allele;
Mendelian inheritance
supertaster - CORRECT ANSWER - homozygous dominant TT
medium tasters - CORRECT ANSWER - heterozygous genotype Tt
Kim et all 2003 - CORRECT ANSWER - located and sequenced TAS2R38 (PTC gene) on
chromosome 7; codes for one of the 25 bitter taste receptor proteins
PAV (proline-alanine-valine) - CORRECT ANSWER - major taster haplotype (T allele)
AVI (alanine-valine-isoleucine) - CORRECT ANSWER - major nontaster haplotype (t
allele)
Miller and Reedy - CORRECT ANSWER - methylene blue solution to stain the anterior
tongue; variations in number of fungiform papillae and tastebuds in individuals (increase in PTC
tasting increased with density of fungiform papillae)
filiform papillae - CORRECT ANSWER - do not contain taste buds; deep blue stain
Questions and CORRECT Answers
objective - CORRECT ANSWER - characterize each student's ability to detect bitterness
using a PTC test strip; assess if response to unsweetened grapefruit juice correlates with PTC test
strip results; determine the density of taste bud-containing fungiform papillae (visual assay of the
anterior aspect of student's tongue; correlate with PTC test strip and grapefruit juice responses);
isolate DNA (saline mouth wash extraction), PCR amplify and (HaeIII restriction enzyme) digest
a short region of the TAS2R38 gene from each student to determine student genotype; Assess if
there is a relationship between genotype (TAS2R38 alleles) and phenotype (taste bud density,
response to PTC strip, grapefruit juice); examine the relationship between bitterness tasting
ability, avoidance of bitter tasting foods and incidence of cancer
five basic tastes - CORRECT ANSWER - sweet
sour
bitter
salty
umami (MSG L-form)
How does taste work? - CORRECT ANSWER - 1. taste molecule binds to receptor on
taste cell
2. cell generates a nervous impulse which is interpreted by the brain
*taste sensation is determined by wiring, not by which type of molecule is bound
phenylthiocarbamide (PTC) dust - CORRECT ANSWER - Arthur Fox tasted nothing, CR
Noller tasted bitterness
Albert Blakeslee - CORRECT ANSWER - inability to taste PTC is a recessive trait in
human populations (tasters 75%, nontasters 25%)
How many genes for bitter taste receptors? - CORRECT ANSWER - 30
, gene for PTC taste receptor - CORRECT ANSWER - TAS2R38; three SNPs correlate with
bitter tasting ability (five different haplotypes)
haplotype - CORRECT ANSWER - a specific combination of SNPs that correlates with a
trait
SNPs in serotonin transporter/receptor genes - CORRECT ANSWER - predict adverse
responses to anti-depression drugs (PROZAC/Paxil)
ability to taste PTC - CORRECT ANSWER - presence of at least one dominant allele;
Mendelian inheritance
supertaster - CORRECT ANSWER - homozygous dominant TT
medium tasters - CORRECT ANSWER - heterozygous genotype Tt
Kim et all 2003 - CORRECT ANSWER - located and sequenced TAS2R38 (PTC gene) on
chromosome 7; codes for one of the 25 bitter taste receptor proteins
PAV (proline-alanine-valine) - CORRECT ANSWER - major taster haplotype (T allele)
AVI (alanine-valine-isoleucine) - CORRECT ANSWER - major nontaster haplotype (t
allele)
Miller and Reedy - CORRECT ANSWER - methylene blue solution to stain the anterior
tongue; variations in number of fungiform papillae and tastebuds in individuals (increase in PTC
tasting increased with density of fungiform papillae)
filiform papillae - CORRECT ANSWER - do not contain taste buds; deep blue stain
