Taste buds consist of 50 to 150 taste bud cells. On the surface of taste cells, there are many taste receptors. When different substances bind to different receptors, our brains can feel different tastes.
What kind of molecular structure can combine with receptors on the surface of taste cells to send a "sweet" signal to the brain? For a long time, people have been trying to figure out this problem, but up to now, this mystery has not been completely solved.
Most scholars believe that sugar is sweet, because all saccharides contain polyhydroxy groups. In polyhydroxy groups, there is a certain distance between two hydrogen atoms, which is only a chemical match with the taste receptors on the tongue. This chemical anastomosis can stimulate the taste receptors to produce pulses, which are then transmitted from the nerves to the brain, making people feel sweet.
For example, ethanol is not sweet, but ethylene glycol is sweet. There is a sweet unit in the molecular structure of ethylene glycol, but it is not sweet because there is no such group in the molecular structure of ethanol. The molecular structure of glucose and mammary gland also contains this sweet unit, so it is also sweet.
The tip of the tongue is most sensitive to sweetness. When sugar touches the taste cells on the tip of the tongue, the -OH in the sweetness unit combines with -—NH2 in the sweetness perception protein on the tip of the tongue to form hydrogen bonds, thus giving people a sweet feeling.
But the sweetness of various sugars is different, because single or double hydrogen bonds can be formed inside the sugar. Therefore, not all sugars are sweet, such as starch, glycogen and cellulose.
Biological mechanism of sweetness formation in extended data;
Sweetness usually refers to the pleasant feeling caused by sugar. Some protein and other non-sugar special substances can also cause sweetness. Sweetness is usually related to aldehyde groups and ketone groups attached to carbonyl groups. Sweetness is obtained through a variety of G protein-coupled receptors, which are coupled with G protein taste receptors existing in taste buds.
The reflection principle of sweetness:
The stimulation received by the taste receptors in the first two-thirds of the tongue is transmitted through the tympanic cord of facial nerve; The taste of retroglossal13 is transmitted by glossopharyngeal nerve; The stimuli received by the taste receptors of retrolingual 1/3, soft palate, pharynx and epiglottitis are transmitted through the vagus nerve. Taste enters the brain stem through the axons of facial nerve, lingual nerve and vagus nerve, and finally changes neurons, and then reaches the insular taste area through thalamus.
The distribution of taste mainly includes: the middle part of the tongue, the root of the tongue, the tip of the tongue and both sides of the tongue.
Sweet nerves are generally distributed in the two wings of the middle tongue. When the nerve cells in this position are stimulated by salty taste, they will be reflected to the brain for processing.
Xinhuanet-Why is sugar sweet?