to the brain.
The diversity of GPCRs allows for a variety of different molecular
shapes to be associated with the taste of bitterness. Among things
that taste bitter are various plant alkaloids such as caffeine, cocaine,
morphine, and quinine—all of which are poisons. Even though every-
thing is a poison, some things are more poisonous than others, anda
bitter taste may serve as a warning that whatever is being ingested is
poisonous and caution is advised. Bitter-tasting things are common in
nature.
Although bitter taste is often experienced as somewhat aversive
(thus inhibiting excessive consumption), it may also be appreciated
as exquisite, especially when it occurs in certain combinations with
other tastes and aromas. Many folks appreciate the bitter taste of
coffee, tea, dark chocolate, tonic water, and leafy vegetables such as
endive and radicchio.
Sweet. This is the defining taste of sugar—sucrose, what we call table
sugar, but also glucose, fructose, lactose, maltose, and many others.
HO HO OH OH H Be OH SenO Yr
HO oO i
ones
SucroseThese are small molecules, composed of chains or rings of carbon
atoms, together with quite a few oxygen atoms and, of course, hydro-
gen atoms.
Sweet receptor proteins are also GPCRs, and two distinct GPCRs
are known in humans to be involved in the detection of sweet-tasting