Taste 1 Lecture 13 Flashcards
What sort of sense is taste and smell?
Chemical sense, This is what module B is about.
Chemicals are either dissolved in water or air and that is how they are tasted or smelt.
What do taste and smell senses have in common?
The sensory inputs merge at the highest level of processing pathway and provide a common sense of flavour that is characteristic of food and drinks we eat
What do animals and humans depend on smell for?
To detect stimuli of food, noxious stimuli and potential mates.
What are the senses of taste and smell connected with?
Basic internal needs including thirst, hunger, emotion and certain forms of memory
Amagdyla, hippocampus extensions from the processing pathways.
Describe the pathways of the taste and smell
Neural information fro each pathway is processed in parallel and merged at higher levels in the cerebral cortex.
What are the types of papillae, their size, location and innervation?
Papillae:
- Circumvallet, large, back of tongue, cranial nerve IX (glossopharyngeal)
- Foliate Papillae, sides of tongue, Mixed innervation
- Fungiform papillae, small, 2/3 front tongue, innervation from VII CN, (facial)
What do papillae contain?
They all contain different taste receptors that can detect certain tastes. The receptors are randomly spread and the tongue is not divided into taste areas.
(papillae contain taste buds, which are made up of taste cells)
Describe how many taste buds humans, have and their distribution amongst papillae:
~4000 in total
Circumvallet have hundreds of taste buds per papillae.
Foliate have dozens-hundreds
Fungiform have 1-4 per
Describe the position of taste buds on papillae
There are trenches down the sides of the papillae and this is where the taste receptors are located. Saliva and food mixes down here.
Saliva is essential for taste recognition.
Describe the anatomy of a papillae:
Papillae contain taste buds
Taste buds are made up of taste cells, 50-150 per bud.
Taste cells form onion like structures.
Taste cells have taste receptors
What do taste cells synapse with?
The gustatory afferent axons.
Describe taste cells and the onion like structure.
Taste cells are bipolar and have microvilli that come together to form a taste pore on the surface of the bud. This is where food interacts.
Supporting cells provide metabolic and structural support to the taste cells.
Basal cells are stem cells that will proliferate to replace dying taste cels.
All these cells are found in the onion like structure..
What is the time life of a taste cell?
Two weeks therefore basal cells are very active.
What are the types of taste receptors in terms of functional classification
3 g coupled protein receptors
2 ion channels
Where else can taste receptors be found?
Gut, pancreas and lungs
What are the five major tastes?
Sweet Salty Sour Bitter Umami
What are the ligands for the five major tastes?
Sweet = Glucose/sugars/sweetners Salty = Na Sour = H Bitter = Quinine and others Umami = Amino Acids
What do the five major taste ligand inform us of?
Sweet = Energy Salty = Ionic Sour = Changed pH (rotting food warning) Bitter = toxic warning Umami = protein
What is the umami receptor protein composition?
Herterodimer of T1R1 + T1R3
What is the sweet receptor
Heterodimer of T1R2 +T1R3
What is an allosteric modulator of umami receptors?
IMP, GMP, AMP Therefore enhance tastents.
Whats another tasting of umami receptor?
L-glutamate
What else can active sweet receptors other than sugar?
D orientation amino acids
What allosterically modulates sweet receptors?
Sweet proteins i.e curculin
What protein is the bitter receptors?
T2R… many variants i.e T2R20 or T2R3
each variant is responsible for a specific taste
What protein is sour receptors?
PKD2L1 proteins ion channels (acid responsive)
What receptors are salt receptors?
Epithelial Na channels ENAK
What are the two major types of receptors?
1) Inotropic (Na, H)
2) Metabotropic
Describe the transduction of inotropic receptors?
Depolarisation of the cell by opening the voltage gated (Na,Ca) channels and then neurotransmitter release.
How does the transduction of the metabotropic g protein couples receptors function?
Ligand binds, G protein (different types) all ultimately result in the activation of secondary messengers. These cause depolarisation of the cell and opening of voltage gated ion channels and release of Ca from the SR. Then neurotransmitter release.
Describe specifically Na salty transaction:
Na enters via Epithelial Na channel. This depolarises the cell and causes activation of voltage gated Ca channels. Ca influxes and causes synaptic transmission.
Describe sourness transduction:
H influxes through the PKD2DL ion channel receptor or through the Na channel. This will result in cell depolarisation and inhibitor of K channels by H. This causes cell depolarisation and activation of voltage gated Ca channels and neurotransmitter release.
How is sweetness transduced with sugar?
Sugar binds to the T1R2 + T1R3 receptor. This activates the Gs protein. This activates adenylate cyclase. This produces cAMP. This can activate PKA. This can phosphorylate K channels and prevent K efflux. Cell depolarises which activate voltage gated Ca channels.
Describe sweetness transduction with sweetners?.
Sweetness bind to T1R2 + T1R3 receptor. This activates Gq protein. This activates Phospholipase c. PLC will activate either DAG or IP3.
- DAG activates PKC, phosphorylates K channel, cell depolarises etc
- IP3 releases Ca from Ca stores. and this results in TRPM 5 channels activation and Ca influx. etc
Thus neurotransmitter release.
Describe umami transduction
Some amino acid will bind to its own receptor i.e arginine will bind to the arg receptor. This causes cell depolarisation and opening of voltage gated Ca channels. and neurotransmitter release.
However most amino acids act on T1R1 + T1R3 receptor. This causes Alpha gustducin to active PDE. Hydrolyses cAMP. Ca channels are no loner disinhibited and Ca stores open.
Alternatively A-gustducin has beta and gamma sub units. B subunit can activate PDE beta. Which activates DAG and IP3 which acts on the same mechanisms previously stated.
- DAG activates PKC, phosphorylates K channel, cell depolarises etc
- IP3 releases Ca from Ca stores. and this results in TRPM 5 channels activation and Ca influx. etc
How is bitterness transduced?
Sime bitter compounds i.e. quinine inactive K channels and this causes cell depolarisation. Ca entry and neurotransmitter release. (Voltage gated Ca channels)
Most bitter compounds act on T2R rece.ptors. Activates Alpha gustducin as a a g protein.
Thus active PDE. Hydrolyses cAMP. Ca channels are no loner disinhibited and Ca stores open.
Alternatively A-gustducin has beta and gamma sub units. B subunit can activate PDE beta. Which activates DAG and IP3 which acts on the same mechanisms previously stated.
- DAG activates PKC, phosphorylates K channel, cell depolarises etc
- IP3 releases Ca from Ca stores. and this results in TRPM 5 channels activation and Ca influx. etc
What two transduction pathways are identical apart form the receptors?
Umami and bitter!
How can cells tell the difference between bitter and umami if they have the same intracellular signalling pathways?
Bitter and umami receptors are never expressed in the same cell.
Describe the molecular structure of T1R
7 transmembrane domains
Extracellular N terminal (loop) - Can be in closed or open conformation.
Structure deduced from mutagenesis studies.
Venous fly trap motif for ligand binding
Other than glucose what can bind to the sweet receptors and how are they different?
Sweet proteins i.e Miraculin bind to the outside of the receptor, In response to a change in extracellular pH they cause the receptor to become a closed conformation and therefore cause the signalling thus lemons can taste very sweet.
Why do some foods taste so good?
taste synergy
What is taste synergy?
When certain foods contain the same compounds that activate a receptor i.e tomatoes and cheese contain glutamate. As well as IMP-an allosteric modulator. Which enhance the taste! thus making more tasty!
What is taste synergy used in?
Chewing gum and artificial sweeteners.
What is an example of a taste receptor that some people have and others don’t?
T2R38. responsive to PTC. Bad taste.
Some people are blind to this taste
Genetic predisposition
What do super tasters have more of?
Papillae
How many people are super tasters?
25%, 50% normal, 25% poor tasters.
