Weeks 4 & 5 Flashcards
1
Q
What is the sweet receptor?
A
T1R2+3
2
Q
What is the umami receptor?
A
T1R1+3
3
Q
True or false: sweet and amino acid (umami) taste share a common receptor and evolutionary origin
A
True
4
Q
Describe the T1r2+T1r3 heterodimer
A
5
Q
T1Rs mediate sweet taste by forming heterodimeric
A
- GPCRs
- TwR3 homodimers (may have very low sweet response)
- T1R2/T1R3 heterodimers
6
Q
These are a family of seven-transmembrane proteins that form heterodimeric GPCRs
A
T1Rs
7
Q
What are two pieces of evidence that T1Rs mediate sweet taste?
A
- expression studies in heterologous cells
- T1R3 combines with T1R2 (T1R2+3) to form a sweet receptor to respond to sweet taste
- natural sugars
- artificial sweeteners
- sweet proteins
8
Q
The primary (natural) sweet testants in the human diet are
A
sugars
9
Q
What is another thing in addition to sugar that has sweet taste?
A
amino acids
10
Q
What three amino acids do humans find the sweetest?
A
- alanine
- glycine
- serine
11
Q
What is a good sweet stimulus in mice?
A
D-tryptophan
12
Q
These are a short chain of carbohydrates
A
sugar
13
Q
What is the basic formula of a sugar?
A
14
Q
Other than sugar, what are two other primary classes of carbs?
A
- starch
- fiber
15
Q
What are the 3 monosaccarides?
A
- glucose (aka dextrose)
- fructose (aka fruit sugar)
- galactose
16
Q
This monosaccharide is produced by plants through photosynthesis and is the energy source for living organisms
A
glucose aka dextrose
17
Q
Glucose is also known as
A
dextrose
18
Q
This is the sweetest naturally occurring sugar
A
fructose aka fruit sugar
19
Q
Fructose is also known as
A
fruit sugar
20
Q
This monosaccharide is most commonly found naturally in lactose
A
galactose
21
Q
What two sugars make up lactose?
A
glucose and galactose
22
Q
What are fructose and galactose metabolized to?
A
glucose
23
Q
When most people are referring to sugar, they are talking about
A
sucrose
24
Q
What two things produce table sugar?
A
- plants
- cyanobacteria
25
Most fruits taste sweet because they contain what two things?
1. fructose
2. sucrose
26
Order the monosaccharides from least sweet to sweetest.
Glucose --> sucrose --> fructose
27
Sucrose will break down into a solution of 50/50
glucose/fructose
glucose:fructose
28
What is corn syrup?
corn syrup made from the starch of corn (aka maize)
29
What 3 things make up high fructose corn syrup?
1. water
2. maltose
3. larger oligosaccharides
30
What happens to high fructose corn syrup before use?
enzymatically treated to break down most of the oligosaccharides to glucose (~90%)
31
How do you make high fructose corn syrup?
xylose isomerase is used to convert glucose to fructose
32
splenda
sucralose
33
table sugar
sucrose
34
Artificial sweetener packets combine what to sugars?
dextrose and maltodetrix
35
True or false: Artificial sweeteners are 2 x sweeter than sugar
True
36
How do taste cells detect sweet compounds (i.e., what is the primary detector for sweeteners)?
T1r2+T1r3
37
Is the T1r2+T1r3 the only sweet detector?
some sugars are also detected by other means
38
What are glucose transporters and Katp metabolic sensor channels doing in the taste cells?
they underlie a T1r-independent sweet pathway for detecting sugars
39
Describe the downstream signalling of T1Rs and T2Rs
40
What are the two pieces of evidence that T1Rs and T2Rs share a common signalling pathway?
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
Is there data to suggest that taste receptor cells only express receptors for 1 taste modality?
Yes
42
How do T1r3 knockout mice respond to non-caloric sweetners?
lack behavioural and nerve responses
43
How do T1r3 knockout mice respond to sugars?
retain behavioural response to sugars
44
Is the T1r2+T1r3 receptor the only sweet detector?
some sugars are detected by other means
45
What are glucose transporters and Katp metabolic sensor channels doing in taste cells?
probably underlie the T1r-independent sweet pathway for detecting sugars
46
Describe the metabolic pathway that mediates sweet-detecting taste cells in T1r3-independent sugar sensing.
47
What 5 steps are involved in the putative metabolic transduction mechanism for sugars?
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
Taste cell expressed intestinal brush border enzymes can convert sucrose into
fructose and glucose
49
What happens after sucrose is converted into fructose and glucose?
glucose is transported into sweet detecting taste cells and generates ATP
50
Describe the brush border enzyme functions
51
What is the strongest aversive taste quality which is believed to be tuned towards the detection of potential poisons?
bitter taste
52
How many bitter taste receptors are there?
~30 T2Rs
53
True or false: T2Rs only respond to one bitter compound
False, some T2Rs only respond to 1 bitter compound but others can respond to more than 50 bitter compunds
54
Bitter taste is mediated by the activation of specific receptors, called
TAS2R genes
55
Where are TAS2R genes found?
all vertebrates from fish (<10) to humans (25)
56
any agent which, when introduced into an animal organism, is capable of producing a morbid, noxious or deadly effect
poison
57
True or false: Everything is a poison when taken in high enough doses
True
58
What are the 4 origins of bitter substances?
1. plants (primary)
2. animals
3. food spoilage
4. man-made drugs
59
What are the 2 pieces of evidence that T2Rs mediate bitter taste?
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
Differences in the sensitivity to bitter compounds between species is likely to be a reflection of
sequence diferences in T2Rs
61
What is the evidence that T2Rs mediate bitter taste in humans?
human T2Rs confer sensitivity to bitter compounds that mice are normally insensitive to
62
What were the first two discoveries of umami?
1. kelp
2. dried bonito flakes
63
True or false: Sweet and amino acid (umami) tastes share a common receptor and evolutionary origin
True
64
What is an example of heteromeric GPCRs changing selectivity based on combinatorial arrangement of subunits
umami T1R1+3
65
The T1Rs mediating umami taste are composed of what 3 things?
1. GPCRs
2. T1R1/T1R3
3. Broadly tuned amino-acid receptor
66
What food contains glutamate, umami taste?
67
What amino acid comprises the highest composition in chickens?
glutamate
68
What amino acid comprises the highest composition in tomatoes?
glutamate
69
What amino acid comprises the highest composition in wheat flour and soy beans?
glutamate
70
What 2 amino acids are involved in umami taste?
1. glutamate
2. aspartate
71
What 7 amino acids are involved in sweet taste?
1. glycine
2. alanine
3. serine
4. threonine
5. glutamine
6. asparagine
7. proline
72
What 11 amino acids are involved in bitter taste?
1. valine
2. leucine
3. isoleucine
4. phenylalanine
5. tyrosine
6. histidine
7. lysine
8. argininte
9. cysteine
10. methionine
11. tryptophan
73
What receptor mediates both sweet and umami taste?
T1Rs
74
In knockout mice, what specifically reduces umami responses?
mGluR4
