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CTB > Taste signalling > Flashcards

Taste signalling Flashcards

1
Q

How many transmembrane helices in GPCRs?

A

7

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2
Q

Define taste

A

taste is used to describe sensations arising predominantly from the oral cavity

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3
Q

What type of signal is the sense of taste?

A

a chemosensory signal mediated by the tongue

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4
Q

Taste buds open into the oral cavity through a __ __

A

taste pore

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5
Q

Taste buds are most prevalent on epithelium of the tongue called ____

A

papillae - although also present on palate, pharynx, and larynx

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6
Q

Where is the highest conc of taste buds?

A

side and back of tongue

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7
Q

What papillae are present on the anterior part of the tongue?

A

Fungiform papillae, which contain 0-15 taste buds

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8
Q

What papillae are present on the posterior portion of the tongue? How many taste buds do they contain?

A

Foliate and circumvallate papillae contain dozens of tastebuds

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9
Q

2 types of cells in taste buds

A
  1. basal cells - small round cells at the base of taste buds
  2. elongated cells - stretch from base to apical end, possess microvilli and have 3 types [I (glial like), II and III (presynaptic cells)]
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10
Q

Taste receptor cells (TRCs) are what kinds of taste bud cells?

A

Type II cells (elongated)

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11
Q

If taste sensation is lost, it returns quickly. Why?

A

Due to high turnover of TRCs. Avg lifespan = 10-11 days

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12
Q

5 conventional tastes

A

sweet, bitter, sour, salt, and umami

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13
Q

What does each taste indicate?

A
  • Sweet - indicates energy-rich nutrients (carbs)
  • Bitter - allows sensing of natural toxins
  • Sour - the taste of acids
  • salt - For electrolyte balance
  • Umami - the taste of amino acids (eg. meat broth)
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14
Q

What are you actually sensing when eating spicy foods?

A

Sensing pain (nociception). CAPSAICIN activates nociceptors

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15
Q

When you see T2, you know that it’s for __ receptors

A

bitter

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16
Q

Receptors for sweet sensation

A

T1R2 + T1R3

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17
Q

Receptors for umami

A

T1R1 + T1R3

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18
Q

Receptor for bitter

A

T2R

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19
Q

Two new taste-coding mdoels

A
  1. labelled-line model: each TRC responds to single taste modality
  2. Across-fiber model: Each TRC responds to multiple taste modalities
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20
Q

What molecule is increased when sugar is eaten? What about when something bitter is eaten?

A 
sweet = cAMP
bitter = calcium
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21
Q

T/F: humans can taste longer chain oligo- and polysaccharides

A

false. Humans can only taste mono and disaccharides

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22
Q

what occurred when sweet taste receptor was blocked by lactisole (a known sweet inhibitor)? What does this suggest

A

Subjects could not detect sweet substances (glucose, matose, sucralose), but they could still detect the glucose oligomers.
This suggests that glucose oligomer detection is independent of T1R2/T1R3 sweet taste receptor. Oigomers were described as “starchy”

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23
Q

Which taste receptor gene is expressed in ALL types of taste buds?

A

T1R3

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24
Q

Which taste receptor gene is predominantly expressed in fungiform and palate taste buds, less so in foliate taste buds, and rarely in circumvallate taste buds?

A

T1R1

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25
Q

T1R2 gene is predominantly expressed in _____ and ___- taste buds

A

circumvallate and foliate. Less so in palate taste buds and rarely in fungiform taste buds

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26
Q

which two taste receptor genes are rarely coexpressed in the same TRC?

A

T1R1 and T1R2

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27
Q

What has bitter taste evolved as?

A

a central warning system against the ingestion of potentially toxic substances

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28
Q

Are T1R genes coexpressed with T2R genes in a single TRC?

A

No

29
Q

Position of ligand binding in T1R vs T2R receptors

A

for T2Rs, ligand binds inside the helices.

For T1Rs, it binds to its N-terminus (has a longer N-terminus compared to T2Rs)

30
Q

Umami is the taste of _____

A

MSG

31
Q

The receptors that encode umami taste include both ___ and ___

A

GPCRs and NMDR receptor ion channels

32
Q

Salt taste sensation is mediated by:

A

ion channels

33
Q

Flavour = ___ + ___

A

taste + olfaction

34
Q

What percentage of GPCRs are for olfaction in humans?

A

50%

35
Q

efficacy of a compound refers to what?

A

its ability to activate receptors to a degree

36
Q

How many T2Rs have been identified in the human genome?

A

25

37
Q

T2Rs in the gastric and intestinal mucosa do what?

A

act as a second line of defence that determine whether ingested substances are beneficial or harmful. They either initiate digestion and absorption or induce vomiting and aversive behaviour

38
Q

What happens when bitter compounds enter the lungs?

A

bitter compounds increase the intracellular calcium ion concentration and stimulate ciliary beat frequency. This is a defense mechanism to eliminate the offending compound.

39
Q

How are bitter compounds used in asthma?

A

bitter tastants cause RELAXATION of isolated airway smooth muscle and dilation of arways. Bitter tastants decreased airway obstruction

40
Q

The human bitter receptor, T2R38, is known as the ___ receptor

A

PTC (phenylthiocarbamide)

41
Q

Humans are categorized into tasters and non-tasters based on their ability to taste ___

A

PTC. Ability to taste PTC is a dominant genetic trait

42
Q

The two forms of T2R38, designated as taster and non-taster, differ from each other how?

A

at three amino-acid positions

43
Q

Genotypes of tasters, non-tasters, and supertasters

A

Supertasters: PAV/PAV
Taster: PAV/AVI
Nontaster: AVI/AVI

44
Q

what happens in homozygous PAV/PAV individuals

A

they have the ability to sense PTS and PROP as intensely bitter

45
Q

What 3 amino acids are contained by a functional T2R38?

A

PAV: proline, alanine and valine

46
Q

Nasal chemosensory cells use bitter taste signaling to detect:

A

irritants and bacterial signals

47
Q

Inhalation of a bitter antibiotic can have additional effects?

A

yes. Could activate bitter receptors, increasing intracellular calcium and possibly an inflammatory response

48
Q

What kind of papillae are present in more abundance in supertasters?

A

fungiform

49
Q

Single nuceotide changes/mutations are known as

A

single nucleotide polymorphism (SNP)

50
Q

What are sSNPs and nsSNPs?

A

sSNPs (synonymous) are due to mutation in DNA sequence but not in amino acid sequence.
nsSNPs (non-synonymous) are due to mutation in DNA sequene that causes change in amino acid sequence.

51
Q

nsSNPs in T2R38 and T1R2 is associated with what?

A

higher caries risk in children

52
Q

Relationship between PAV/PAV genotype and rheumatoid arthritis

A

Sueprtasters (PAV/PAV) have an enhanced immune response and fight disease better. This becomes a problem with age, as the immune system may become “rogue” and cause autoimmune disorders such as RA

53
Q

Do supertasters have a greater or lesser risk of childhood caries?

A

lesser

54
Q

Why can’t you feed dogs xylitol?

A

Because dogs produce insulin when they eat xylitol (humans do not) and can become hypoglycemic. Could be deadly

55
Q

Antagonist or inverse agonists of T2Rs are referred to as ____

A

bitter blockers or bitter taste blockers

56
Q

Fade vs tachyphylaxis vs desensitization

A

Fade: decline in response in the CONTINUED presence of agonist
Tachyphyllaxis: decline in response to REPEATED application of agonist
Desensitization: fade or tachyphylxis in a direct consequence of receptor activation

these are overlapping terms

57
Q

What causes taste signal termination?

A

arrestins bind to the desensitized receptors and uncouple the bound G-protein

58
Q

2 possible mechanisms of T2R desensitization:

A
  • Receptor desensitization

- activation of arrestin

59
Q

Aging as a factor affecting taste perception

A

with age, number of taste buds in the oral cavity decrease

60
Q

How does smoking affect taste?

A

causes taste loss due to desensitization of bitter receptors

61
Q

What is geusia?

A

sense of taste

62
Q

3 main types of geusia

A
  1. Ageusia: complete lack of taste
  2. Hypogeusia: deacreasi in taste sensitivity
  3. Dysgeusia: distortion/changes in taste sensitivity
63
Q

what kind of supplements have been shown to help patients with dysgeusia?

A

zinc supplementation

64
Q

What symptoms related to taste do patients with familial dysautonomia display?

A

inability to taste.

Absence of taste buds and a paucity of sensory nerves in the tongue

65
Q

What is Bell’s palsy and how does it affect taste?

A

Bell’s palsy is a form of temporary facial paralysis resulting from damage to the facial nerve due to viral infection by viral meningitis or herpes simplex.
Symptoms may include dry mouth and impairment of taste mostly on one side of the tongue

66
Q

What is Sjogren’s syndrome?

A

an autoimmune disorder in which immune cells attack and destroy glands that produce tears and saliva.

67
Q

What is Wallenberg’s syndrome?

A

neurological condition caused by a stroke. Symptoms include dicfficulty swallowing, nausea and vomiting. Some individuals LOSE THEIR SENSE OF TASTE ON ONE SIDE OF THE TONGUE, while preserving taste on the other side.

68
Q

Which nerve can be damaged during a third molar extraction and what affect can this have?

A

chorda tympani. Damage can lead to temporary loss of taste perception (up to 6 months)

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