Reading Test 1

11 | 
P a g e
 
California School of Medicine at San Diego. “Every other species is averse to bitter 
because it means bad news. But we have learned to enjoy it. We drink coffee, which is 
bitter, and quinine [in tonic water] too. We enjoy having that spice in our lives.” Because 
bitterness can be pleasing in small quantities but repellent when intense, bitter blockers 
like AMP could make a whole range of foods, drinks, and medicines more palatable-and 
therefore more profitable. 
D
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People have varying capacities for tasting bitterness, and the differences appear to be 
genetic. About 75 percent of people are sensitive to the taste of the bitter compounds 
phenylthiocarbamide and 6-n-propylthiouracil. and 25 percent are insensitive. Those who 
are sensitive to phenylthiocarbamide seem to be less likely than others to eat cruciferous 
vegetables, according to Stephen Wooding, a geneticist at the University of Utah. Some 
people, known as supertasters, are especially sensitive to 6-n-propylthiouraci because 
they have an unusually high number of taste buds. Supertasters tend to shun all kinds of 
bitter-tasting things, including vegetable, coffee, and dark chocolate. Perhaps as a result, 
they tend to be thin. They’re also less fond of alcoholic drinks, which are often slightly 
bitter. Dewar’s scotch, for instance, tastes somewhat sweet to most people. ” But a 
supe
rtaster tastes no sweetness at all, only bitterness,” says Valerie Duffy, an associate 
professor of dietetics at the University of Connecticut at Storrs. 
E.
In one recent study, Duffy found that supertasters consume alcoholic beverages, on 
average, only two to three times a week, compared with five or six times for the average 
nontasters. Each taste bud, which looks like an onion, consists of 50 to 100 elongated 
cells running from the top of the bud to the bottom. At the top is a little clump of receptors 
that capture the taste molecules, known as tastants, in food and drink. The receptors 
function much like those for sight and smell. Once a bitter signal has been received, it is 
relayed via proteins known as G proteins. The G protein involved in the perception of 
bitterness, sweetness, and umami was identified in the early 1990s by Linguagen’s 
founder, Robert Margolskee, at Mount Sinai School of Medicine in New York City. Known 
as gustducin, the protein triggers a cascade of chemical reactions that lead to changes in 
ion concentrations within the cell. Ultimately, this delivers a signal to the brain that 
registers as bitter. “The signaling system is like a bucket brigade,” Margolskee says. “It 
goes from the G protein to other proteins.” 
F
.
In 2000 Zuker and others found some 30 different kinds of genes that code for bitter-taste 
receptors. “We knew the number would have to be large because there is such a large 
universe of bitter tastants,” Zuker says. Yet no matter which tastant enters the mouth or 
which receptor it attaches to, bitter always tastes the same to us. The only variation 
derives from its intensity and the ways in which it can be flavored by the sense of smell. 
“Taste cells are like a light switch,” Zuker says. “They are either on or off.” 

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