Lecture 2

Question 1

Gustation

Answer 1

taste
- to identify food, avoid noxious/toxic food

Question 2

5 dimensions of taste

Answer 2

sweet,sour, bitter, salty, umami

Question 3

free protons

Answer 3

H+ - acidic

Question 4

umami

Answer 4

• sensation induced by glutamate
• ‘savory tast’ -‘meaty’‘brothy’

e.g. soy sauce, msg

Question 5

what does umami indicate

Answer 5

high protein

Question 6

anatomical units of gustation

Answer 6

• taste buds embedded in epithelium of tongue

Question 7

taste buds

Answer 7

~10 taste cells
- opening on top of taste buds allows cells to be activated

Question 8

cells in taste buds

Answer 8

• Type I cell (glial)
• Type II cell
• Type III cell

Question 9

Type II & III cells

Answer 9

• only signal within taste bud, not directly to brain
• neurons respond to stimulant in taste bud with graded changes in polarisation (depolarisation) and neurotransmitter release

Question 10

depolarisation

Answer 10

occurs when stimulant enters cell, cations move in, more neurotransmitter released

• sodium/ potassium exchanger

Question 11

resting potential sodium/potassium exchanger

Answer 11

• high intracellular potassium
• high extracellular sodium

Question 12

synaptic release

Answer 12

• voltage gated sodium and calcium channels for depolarisation and neurotransmitter release

Question 13

type III cells

Answer 13

sour

Question 14

type II cells

Answer 14

• bitter
• sweet
• umami

Question 15

type II cells: GPCRs

Answer 15

• G protein Gustducin: Gβγ
• beta/gamma subunit goes off and activates phospholipase C
• PLC catalyses PIP2->IP3+DAG

Question 16

IP3

Answer 16

inosotyl triphosphate

Question 17

DAG

Answer 17

Diacylglycerol

Question 18

IP3 as second messanger

Answer 18

• binds to and activates receptor on endoplasmic reticulum
• leads to calcium leaving ER and entering cytosol, depolarising neuron

Question 19

what is calcium detected by in taste buds

Answer 19

cation channel -TRPM5

Question 20

TRPM5

Answer 20

opens when Ca content high in cell, and allows more cations in e.g. Na, depolarisation

Question 21

Type II cells summary

Answer 21

• receptor activation
• activates G protein gustducin
• b/y interact with PLC
• PLC increases IP3 and DAG
• IPS activates receptors on endoplasmic reticulum to allow calcium to leave ER to cytosol
• increased Ca, leads to TRPM5 channel opening, letting cations into neuron
• neurons depolarise

Question 22

Type II cells specificity to detect ‘sweet’

Answer 22

• sucurose, fructose, aa etc
• GPCR T1R2:T13
• hetero dimer to detect sweet

Question 23

Type II cells specificity to detect ‘umami’

Answer 23

• option 1: hetero dimer T1R1:T1R3
• option 2: ‘conventional’ metabotropic glutamate receptors
  mGluR1/mGlur4

Question 24

Type II cells specificity to detect ‘bitter’

Answer 24

• variety of natural and synthetic compounds
• T2R
• ~30 genes

Question 25

Type III cells: sour

Answer 25

• organic acids e.g. citric and acetic acids
• pH sensitive K+ leakage channel