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Taste > Weeks 4 & 5 > Flashcards

Weeks 4 & 5 Flashcards

1
Q

What is the sweet receptor?

A

T1R2+3

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2
Q

What is the umami receptor?

A

T1R1+3

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3
Q

True or false: sweet and amino acid (umami) taste share a common receptor and evolutionary origin

A

True

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4
Q

Describe the T1r2+T1r3 heterodimer

A
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5
Q

T1Rs mediate sweet taste by forming heterodimeric

A
  1. GPCRs
  2. TwR3 homodimers (may have very low sweet response)
  3. T1R2/T1R3 heterodimers
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6
Q

These are a family of seven-transmembrane proteins that form heterodimeric GPCRs

A

T1Rs

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7
Q

What are two pieces of evidence that T1Rs mediate sweet taste?

A
  1. expression studies in heterologous cells
  2. T1R3 combines with T1R2 (T1R2+3) to form a sweet receptor to respond to sweet taste
    - natural sugars
    - artificial sweeteners
    - sweet proteins
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8
Q

The primary (natural) sweet testants in the human diet are

A

sugars

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9
Q

What is another thing in addition to sugar that has sweet taste?

A

amino acids

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10
Q

What three amino acids do humans find the sweetest?

A
  1. alanine
  2. glycine
  3. serine
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11
Q

What is a good sweet stimulus in mice?

A

D-tryptophan

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12
Q

These are a short chain of carbohydrates

A

sugar

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13
Q

What is the basic formula of a sugar?

A
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14
Q

Other than sugar, what are two other primary classes of carbs?

A
  1. starch
  2. fiber
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15
Q

What are the 3 monosaccarides?

A
  1. glucose (aka dextrose)
  2. fructose (aka fruit sugar)
  3. galactose
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16
Q

This monosaccharide is produced by plants through photosynthesis and is the energy source for living organisms

A

glucose aka dextrose

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17
Q

Glucose is also known as

A

dextrose

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18
Q

This is the sweetest naturally occurring sugar

A

fructose aka fruit sugar

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19
Q

Fructose is also known as

A

fruit sugar

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20
Q

This monosaccharide is most commonly found naturally in lactose

A

galactose

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21
Q

What two sugars make up lactose?

A

glucose and galactose

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22
Q

What are fructose and galactose metabolized to?

A

glucose

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23
Q

When most people are referring to sugar, they are talking about

A

sucrose

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24
Q

What two things produce table sugar?

A
  1. plants
  2. cyanobacteria
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25
Q

Most fruits taste sweet because they contain what two things?

A
  1. fructose
  2. sucrose
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26
Q

Order the monosaccharides from least sweet to sweetest.

A

Glucose –> sucrose –> fructose

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27
Q

Sucrose will break down into a solution of 50/50

A

glucose/fructose
glucose:fructose

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28
Q

What is corn syrup?

A

corn syrup made from the starch of corn (aka maize)

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29
Q

What 3 things make up high fructose corn syrup?

A
  1. water
  2. maltose
  3. larger oligosaccharides
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30
Q

What happens to high fructose corn syrup before use?

A

enzymatically treated to break down most of the oligosaccharides to glucose (~90%)

31
Q

How do you make high fructose corn syrup?

A

xylose isomerase is used to convert glucose to fructose

32
Q

splenda

A

sucralose

33
Q

table sugar

A

sucrose

34
Q

Artificial sweetener packets combine what to sugars?

A

dextrose and maltodetrix

35
Q

True or false: Artificial sweeteners are 2 x sweeter than sugar

A

True

36
Q

How do taste cells detect sweet compounds (i.e., what is the primary detector for sweeteners)?

A

T1r2+T1r3

37
Q

Is the T1r2+T1r3 the only sweet detector?

A

some sugars are also detected by other means

38
Q

What are glucose transporters and Katp metabolic sensor channels doing in the taste cells?

A

they underlie a T1r-independent sweet pathway for detecting sugars

39
Q

Describe the downstream signalling of T1Rs and T2Rs

A
40
Q

What are the two pieces of evidence that T1Rs and T2Rs share a common signalling pathway?

A
  1. mouse knockouts of gustucin, PLCB2, or TRPM5 have deficits in sweet, umami, and bitter tastes
  2. salty and sour tastes remain intact in these animals
41
Q

Is there data to suggest that taste receptor cells only express receptors for 1 taste modality?

A

Yes

42
Q

How do T1r3 knockout mice respond to non-caloric sweetners?

A

lack behavioural and nerve responses

43
Q

How do T1r3 knockout mice respond to sugars?

A

retain behavioural response to sugars

44
Q

Is the T1r2+T1r3 receptor the only sweet detector?

A

some sugars are detected by other means

45
Q

What are glucose transporters and Katp metabolic sensor channels doing in taste cells?

A

probably underlie the T1r-independent sweet pathway for detecting sugars

46
Q

Describe the metabolic pathway that mediates sweet-detecting taste cells in T1r3-independent sugar sensing.

A
47
Q

What 5 steps are involved in the putative metabolic transduction mechanism for sugars?

A

Step 1: Enzymes in saliva and on in the membrane of taste cells break more complex carbohydrates down to glucose

Step 2: Glucose transporters pull glucose into the cell

Step 3: Glucose is converted to ATP in the cell

Step 4: ATP shuts down a K+ channel in the membrane, keeping potassium from leaking out

Step 5: Inside of cell de-polarizes, calcium released

48
Q

Taste cell expressed intestinal brush border enzymes can convert sucrose into

A

fructose and glucose

49
Q

What happens after sucrose is converted into fructose and glucose?

A

glucose is transported into sweet detecting taste cells and generates ATP

50
Q

Describe the brush border enzyme functions

A
51
Q

What is the strongest aversive taste quality which is believed to be tuned towards the detection of potential poisons?

A

bitter taste

52
Q

How many bitter taste receptors are there?

A

~30 T2Rs

53
Q

True or false: T2Rs only respond to one bitter compound

A

False, some T2Rs only respond to 1 bitter compound but others can respond to more than 50 bitter compunds

54
Q

Bitter taste is mediated by the activation of specific receptors, called

A

TAS2R genes

55
Q

Where are TAS2R genes found?

A

all vertebrates from fish (<10) to humans (25)

56
Q

any agent which, when introduced into an animal organism, is capable of producing a morbid, noxious or deadly effect

A

poison

57
Q

True or false: Everything is a poison when taken in high enough doses

A

True

58
Q

What are the 4 origins of bitter substances?

A
  1. plants (primary)
  2. animals
  3. food spoilage
  4. man-made drugs
59
Q

What are the 2 pieces of evidence that T2Rs mediate bitter taste?

A
  1. cycoheximide is a bitter compound detected with high affinity by the T2R5 receptor in mice
  2. knockout of T2R5 eliminates taste responses to cycloheximide
60
Q

Differences in the sensitivity to bitter compounds between species is likely to be a reflection of

A

sequence diferences in T2Rs

61
Q

What is the evidence that T2Rs mediate bitter taste in humans?

A

human T2Rs confer sensitivity to bitter compounds that mice are normally insensitive to

62
Q

What were the first two discoveries of umami?

A
  1. kelp
  2. dried bonito flakes
63
Q

True or false: Sweet and amino acid (umami) tastes share a common receptor and evolutionary origin

A

True

64
Q

What is an example of heteromeric GPCRs changing selectivity based on combinatorial arrangement of subunits

A

umami T1R1+3

65
Q

The T1Rs mediating umami taste are composed of what 3 things?

A
  1. GPCRs
  2. T1R1/T1R3
  3. Broadly tuned amino-acid receptor
66
Q

What food contains glutamate, umami taste?

A
67
Q

What amino acid comprises the highest composition in chickens?

A

glutamate

68
Q

What amino acid comprises the highest composition in tomatoes?

A

glutamate

69
Q

What amino acid comprises the highest composition in wheat flour and soy beans?

A

glutamate

70
Q

What 2 amino acids are involved in umami taste?

A
  1. glutamate
  2. aspartate
71
Q

What 7 amino acids are involved in sweet taste?

A
  1. glycine
  2. alanine
  3. serine
  4. threonine
  5. glutamine
  6. asparagine
  7. proline
72
Q

What 11 amino acids are involved in bitter taste?

A
  1. valine
  2. leucine
  3. isoleucine
  4. phenylalanine
  5. tyrosine
  6. histidine
  7. lysine
  8. argininte
  9. cysteine
  10. methionine
  11. tryptophan
73
Q

What receptor mediates both sweet and umami taste?

A

T1Rs

74
Q

In knockout mice, what specifically reduces umami responses?

A

mGluR4

Taste (9 decks)

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