Sweet, Sour, Bitter Sci-Fi

There are five expressions of the human palate: sweet, sour, bitter, salty and umami. Sweet, an evolution to detect energy-rich foods, umami to detect amino acids. Salty for a healthy dietary balance of electrolytes and sour or bitter to warn against ingesting noxious foods.

Specialized taste receptor cells (TRCs) express the different flavor profiles. Scientists are sure TRC’s are the building blocks of taste buds but they can only speculate how receptors communicate the flavor they recognize. They’ve proposed two possible models:

1. The Labelled-Line Model

or

2. The Across-Fiber Model.

In the Labelled-Line Model, taste receptor cells are tuned to express a single flavor profile (sweet, sour, bitter, salty and umami) to their individual connecting fibre. We can imagine the Labelled-Line Model as recognizing your best friend, granted you are in a monogamous best friendship. For example, if Patrick sees Spongebob in a crowd, he will recognize Spongebob and be excited to see him much like if a sour receptor recognized a sour flavor it would perk up and alert the organism of a sour sensation.

Spongebob and Patrick recognize each other as best friends. In this way they exemplify the Labelled-Line Model which suggests TRC’s are specialized cells that recognize a single taste expression (sweet, sour, bitter, salty and umami).

On the other hand, there is also the Across-Fiber Model which suggests one of two theories.

1. A single TRC is tuned to a variety of flavors

Spongebob has many friends which he can recognize in a crowd of strangers, much like in the Across-Fiber Model TRC’s recognize more than one flavor profile.

2. TRC’s recognize a single flavor profile but multiple TRCs communicate with a single connecting fibre which carries all the information for each individual TRC.

Continuing with the Spongebob analogy we have Larry the Lobster. Larry is the lifeguard for Bikini Bottom’s beach so he’s in contact with all  members of the beach community. As the lifeguard, he is the receiver of the beach community’s concerns, even though they may all be different.

Tests support the Labelled-Line model. To quote the reading:

“The ‘taste’ of a sweet or bitter compound (in other words, the perception of sweet or bitter) is a reflection of the selective activation of T1R- versus T2R-express- ing cells, rather than a property of the receptors or even of the tastant molecules. “

Meaning each TRC has it’s own niche. The activation of single cell type is sufficient to trigger taste responses. In tests, scientists (Mueller) engineered mice to express a bitter receptor in sweet cells and found the modified mice showed a strong attraction to bitter compounds despite having shown a strong repulsion to the substance prior. Furthermore, when they were missing certain genes such as T1R2 (sweet gene)-, T2R (bitter)- or PKD2L1 (sour)- they showed extraordinarily specific taste deficits.

Comparable types of gene deficiencies happens in nature. For example, cats don’t have the T1R2 gene so they don’t like sweets. Perhaps in the future, human’s will submit to genetic engineering to rid themselves of their sweet tooth.

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