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BISC 421 - Module II > Taste > Flashcards

Taste Flashcards

1
Q

What are our five tastes?

A
  1. Bitter: toxins (from plants)
  2. Sweet: sucrose (energy source)
  3. Umami: monosodium glutamate (components of protein)
  4. Sour: protons, citrus, acids
  5. Salty: NaCl
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2
Q

Which tastes are aversive? attractive?

A

aversive:
bitter, sour
attractive:
sweet, umami, salty

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3
Q

What is the structure of a taste receptor?

A
  • taste receptor cells do not have axons,

- innervated by fibers originating in taste ganglia that travel in cranial nerves

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4
Q

2 characteristics of taste buds?

A
  • 50-100 taste receptor cells per taste bud

- regenerate continuously throughout adult life

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5
Q

How are different tastes detected? (2)

A
  1. specific receptors detect tastants

2. specific subsets of cells respond to each class of tastants

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6
Q

What was the experiment used to identify the sweet receptor?

A
  • cloned from mouse based on identification of mouse that cannot taste sweet
  • respond to sweet using calcium imaging
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7
Q

In the mouse used to identify sweet receptor, what was the role of calcium?

A

Ca2+ elevation in response to sweet

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8
Q

What are the 2 sweet response receptors?

A

T1R2 and T1R3 coupled to PLCB2 and TRPM5

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9
Q

What is the umami receptor composed of?

A

T1R1 + T1R3

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10
Q

Are receptors Ca2+ permeable?

A

no

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11
Q

What is the cause of the Ca2+ elevation?

A
  • due to coupling of taste receptor to signaling pathway that activate IP3 receptors
  • release Ca2+ from intracellular stores
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12
Q

What are the bitter receptors?

A

-T2Rs

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13
Q

What are 3 qualities of bitter receptors?

A
  1. family of 30 GPCRs
  2. all expressed in same cells
  3. cannot distinguish different bitter tastes
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14
Q

What is the transduction pathway for bitter taste? (8)

A
  1. Ligand binds to receptor, activates G protein
  2. activates PLC
  3. breaks down PIP2 to IP3 + DAG
  4. IP3 opens IP3 receptor/Ca2+ on ER
  5. IC Ca2+ increases
  6. opens TRPM5 ion channel
  7. lets in Na2+
  8. depolarizes taste cells
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15
Q

Which receptor types are unique to taste cells?

A

TRPM5 and PLCB2

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16
Q

Can TPRM5 and PLCB2 Knockouts taste bitter or sweet taste?

A

no

17
Q

Taste Coding (2 models)

A
  1. Cells dedicated to one of 5 tastes, signaling to brainn is hardwired
  2. Cells express mix of receptors, brain sorts it all out
18
Q

What is the PLCB2 rescue experiment?

A
  1. Eliminate all signaling by removing PLCB2 (animal cannot taste, biter, sweet, umami)
  2. Add PLCB2 back under promotor of bitter receptor (transgenic mouse)
  3. Ask: Does this restore sensitivity to sweet?
19
Q

What does yes/no mean for PLCB2 rescue experiment?

A

No: cells that make bitter are different from cells that make sweet (labelled line)
Yes: some cells make bitter and sweet, FALSE

20
Q

What are the 2 elements introduced into a transgenic mouse?

A
  1. promoter

2. transgene

21
Q

What determines whether something tastes good or bad?

A

-Cell type, not receptor

22
Q

What experiment showed what determines whether something tastes good/bad?

A
  • inserted unnatural receptor (RASSL) into T2R expressing cells
  • animals avoid agonist
23
Q

What happens when human specific bitter receptor is put into T2R cell?

A

-animal avoid biter agonist

24
Q

What happens if human bitter receptor in T1R cell?

A

-animal attracted to bitter

25
Q

How are genetic changes made?

A

promoters

26
Q

What is the T1R1 promoter?

A

-T1R1 promoter directs gene to be expressed in umami cell

27
Q

What is the T1R2 promoter?

A

-directs gene to be expressed in sweet cell

28
Q

What is the T2R promoter?

A

-directs genes to be expressed in bitter cell

29
Q

What is so interesting about PTC?

A

-There is polymorphism of whether or not people can taste it.

30
Q

Where is the variation for PTC?

A

-Tas2R38 gene (PAV is taster and AV1 is non taster)

31
Q

What is evidence for balancing selection?

A
  • both tasters and nontasters are found in equal proportions in the populations
  • both alleles must have some selective advantage
32
Q

Are tasters or nontasters dominant?

A

tasters (Mendelian Inheritance)

33
Q

Why can’t cats taste sweet?

A

-T1R2 is a pseudogene in cats meaning it contains inactivating mutations
EX: cats are obligate carnivores

34
Q

What are sour and salty receptors?

A
  • Both are ion channels

- do not use PLCB2 or TRPM5.

BISC 421 - Module II (14 decks)

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