Topic 9 - the chemical senses

Question 1

What are the 5 basic tastes?

Answer 1

Salt, sour, sweet, bitter and Umami (savoury).

Question 2

The tongue is a primary taste organ. Describe the structure of the tongue…

Answer 2

Has ‘dots’ = lingual papillae that contain taste buds ( which are a group of taste cells).

From back of tonue to front(tip) there is Circumvallate, Folliate and Fungiform lingual papille.

• 2000-5000 taste buds
• ~100 chemoreceptive taste cells per taste bud
• Taste pore allows sensory transduction by microvilli

Question 3

What class and type of membrane receptor do the 5 tastes use?

Answer 3

Salt and sour use ion channels:

salt = ion channels = Enac and unknown mechanism 
sour = ion channels = OTOP1

sweet, bitter and umami (savoury) use G-protein coupled receptors:

sweet = T1R2 + T1R3
bitter = T2Rs
Umami (savoury) = T1R1 + T1R3

Question 4

What is the difference between taste cells and taste buds?

Answer 4

taste cells only respond to one stimuli

taste buds have taste cells which respond to various stimuli.

Question 5

What are olfactory receptor cells?

Answer 5

They are bipolar chemoreceptive neurons.

• odorants must dissolve in the mucus layer to reach olfactory receptor cells.
• olafactory receptor cells are regularly replaced in adults.

Question 6

What are ORs?

Answer 6

ORs are odorant receptor proteins: are G protein coupled receptors.

• Olfactory receptor cells only express one type of odorant receptor.
• One odorant receptor can recognise multiple odorants.
• It is the unique combination of odorant receptors that recognise an odorant that allows us to distinguish a specific odor.