Chapter 13 Tongue and Taste

Question 1

taste bud

Answer 1

clusters of receptor cells that begin the process of gustation on the tongue

Question 2

gustation

Answer 2

along with olfaction (the sense of smell), is classified as chemoreception because it functions by reacting with molecular chemical compounds in a given substance. Specialized cells in the gustatory system that are located on the tongue are called taste buds, and they sense tastants (taste molecules).

Question 3

stem cells

Answer 3

similar to the olfactory system, stem cells adjacent to the taste receptor cells can differentiate into the various types of taste receptor cells, characterized by their different taste receptor proteins

Question 4

Gustatory cell replacement

Answer 4

taste receptor cells regularly replaced with a turnover rate of approximately two weeks (presumably related to the fact that these cells are constantly exposed to all kinds of toxic gunk, subject to continual damage)

Question 5

salt

Answer 5

primarily sodium chloride (NaCl)
proteins on taste receptor cells related to the perceptual experience of saltiness are thought to be channels that allow sodium ions to flow across the membrane (thus when a highly concentrated Na+ appears in the mouth after ingestion of salt, the Na+ is believed to flow through sodium ion channels in the salt taste receptor cells, triggering a neural signal to the brain
ionotropic receptor

Question 6

sour

Answer 6

taste of acids: citric acid, acetic acid, lactic acid
defining feature is release of hydrogen ions (H+) in solution
ionotropic receptor

Question 7

bitter

Answer 7

the proteins that initiate the signals associated with the perceptual experience of bitterness are not ion channels; (they are GCPRs)

Question 8

sweet

Answer 8

taste of sugar, sucrose, glucose, fructose, lactose, maltose, etc… (not common in nature)
receptor proteins: GCPR (two distinct are known)
particular molecular shapes of various sugar molecules permit them to bind as ligands to the sweet GPCRs
functional form of the sweet taste receptor protein appears to be a dimer of two GPCRs - the two are linked to form the functional sweet receptor (but two GPCRs associated limit the taste of sweetness)

Question 9

umami

Answer 9

published in 1909 by Japanese chemist Kikunae Ikeda (1864-1936); distinct taste perception (characterized as “savory,” “meaty,” “mushroomy” in seaweeds, fish sauces, soy sauce, dried fish); receptor cells responds to glutamate with taste receptor proteins that are GPCR glutamate receptors

Question 10

taste receptor proteins

Answer 10

ion channels: salt, sour

GPCRs: bitter, sweet, umami

Question 11

sweeter-than-sugar sweeteners

Answer 11

also called nonnutritive (little or no caloric or nutritional value); synthetic (products of the synthetic chemical industry); artificial sweetener (made by human chemists and not found “naturally” in nature)
gave rise to diet foods

Question 12

saccharin

Answer 12

discovered in the late 1800s unintentionally; 300x sweeter than sucrose but has a slightly bitter taste

Question 13

aspartame

Answer 13

most widely used artificial sweetener; 200x sweeter than sucrose

Question 14

Stevia rebaudiana

Answer 14

plant source of a sweeter-than-sugar all-natural sweetener (found in Amazon jungle of South America); appreciated by native inhabitants for sweetness of leaves

Question 15

Gustatory neural pathways

Answer 15

cranial nerve fibers carrying taste sensory information enter the brain via the lower brain stem and connect with cells in the nucleus solitarius, from which two axon tracts emerge (neural activity in these regions of the brain is somehow related to the subjective, perceptual qualities of different tastes, as well as associated emotions)

Question 16

Capsicum annuum

Answer 16

chili plant of South America

Question 17

Capsaicin

Answer 17

molecular constituent associated with the hotness of chili (more present in chili, the hotter the chili is); when capsaicin binds to one of the receptor proteins in the mouth, a shape change occurs, an ion channel opens, and calcium ions flow from outside the cell to inside, depolarizing the cell and leading to increased neural excitability); thermal heat also activates these capsaicin-sensitive proteins; capsaicin receptor proteins are located in the mouth as well as all over the body

Question 18

menthol

Answer 18

molecule from mint plants that characterizes mint flavors, perception of a kind of “coolness”; when menthol binds with an ionotropic receptor protein (found in the mouth and elsewhere in the body) a calcium channel opens

Question 19

isothiocyanates

Answer 19

a family of molecules characterized by a particular configuration of sulfur, carbon, and nitrogen atoms; allyl isothiocyanates found in mustard, horseradish, and wasabi; binding of isothiocyanates to TRPA1 receptor activates another ionotropic Ca++ channel called TRPA1

Question 20

flavor

Answer 20

a combination of several different channels of sensory information; mouth components of taste and pungency are hugely important to the flavor of food and drink; perhaps most important to flavor are aromatic molecules, sensed via the olfactory system

Question 21

TRP channels

Answer 21

located all over the body; associated with a qualitatively different experience of hotness and pungency (example of how when life comes up with a structure possessing useful properties, it gets slightly tweaked and modified)