ACERB
(uh-SURB)
Sour
or bitter to the taste
Common
clues: Caustic;
Sour; Bitter; Biting; Harsh; Sharp-tongued; Tart
Crossword
puzzle frequency:
once a year
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Sourness
Sourness
is the taste that detects acidity. The mechanism for detecting
sour taste is similar to that which detects salt taste. Hydrogen
ion channels detect the concentration of hydronium ions (H3O+
ions) that are formed from acids and water.
Hydrogen
ions are capable of permeating the amiloride-sensitive sodium
channels, but this is not the only mechanism involved in
detecting the quality of sourness. Hydrogen ions also inhibit the
potassium channel, which normally functions to hyperpolarize the
cell. Thus, by a combination of direct intake of hydrogen ions
(which itself depolarizes the cell) and the inhibition of the
hyperpolarizing channel, sourness causes the taste cell to fire
in this specific manner.
Bitterness
The
bitter taste is perceived by many to be unpleasant, sharp, or
disagreeable. Evolutionary biologists have suggested that a
distaste for bitter substances may have evolved as a defense
mechanism against accidental poisoning. Common bitter foods and
beverages include coffee, unsweetened chocolate, bitter melon,
beer, uncured olives, citrus peel, many plants in the
Brassicaceae family, dandelion greens and escarole. Quinine is
also known for its bitter taste and is found in tonic water.
The
most bitter substance known is the synthetic chemical denatonium,
discovered in 1958. It is used as an aversive agent that is added
to toxic substances to prevent accidental ingestion.
Research
has shown that TAS2Rs (taste receptors, type 2) such as TAS2R16
coupled to the G protein gustducin are responsible for the human
ability to taste bitter substances. They are identified not only
by their ability to taste for certain "bitter" ligands,
but also by the morphology of the receptor itself (surface bound,
monomeric). Researchers use two synthetic substances,
phenylthiocarbamide (PTC) and 6-n-propylthiouracil (PROP) to
study the genetics of bitter perception. These two substances
taste bitter to some people, but are virtually tasteless to
others. Among the tasters, some are so-called "supertasters"
to whom PTC and PROP are extremely bitter. This genetic variation
in the ability to taste a substance has been a source of great
interest to those who study genetics. In addition, it is of
interest to those who study evolution since PTC-tasting is
associated with the ability to taste numerous natural bitter
compounds, a large number of which are known to be toxic.
This
article is licensed under the GNU
Free Documentation License.
It uses material from the Wikipedia
article "Taste".
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