B&B Smell and taste

Question 1

What do sensory systems do?

Answer 1

Represent vast information from the environment
This is relevant to animal’s survival and reproduction
Different animal species have different sensory worlds

Question 2

How do tsetse flies taste?

Answer 2

Taste hairs

There are components in sweat that stimulate tarsal taste neurones

Question 3

Describe an insect’s NS

Answer 3

CNS
Visceral nervous system
Peripheral nervous system

Question 4

Describe an insect’s brain

Answer 4

Mushroom body
Located in the protocerebrum
Centre of sensory integration and memory formation
Optic lobe in protocerebrum
Antennal lobe in deutocerebrum
Also, a tritocerebrum

Question 5

What is a sensillum?

Answer 5

A sensory organelle
A companion sensillum is a mechanical stress detector
A typical insect sensillum is one or several bipolarsensory neurones which are tightly enveloped by the glia-like thecogen cell.
This is partly enclosed by the trichogen and tormogen cells

Question 6

How does a sensillum develop?

eg epidermal eg trichogen

Answer 6

Cells arise via differential mitoses from an epidermal sensillum mother cell
The trichogen cell secretes the cuticle of the sensory hair
The tormogen cell forms the hair socket
When the cuticle is formed, both cells retract
They form the subcuticular sensillum lymph cavity and excrete the sensillum lymph

Question 7

The olfactory sensilla that hold the sensory neurones are called?

Answer 7

Olfactory receptor neurones

Found in antennae and in maxillary palps

Question 8

How can the electrical activity of sensory neurones be measured?

Answer 8

Electrophysiological experiments
APs generated by the sensory neurones in response to an odour stimuli are recordered
Electrode and amplifier

Question 9

Describe a dose response curve

Answer 9

Physiological responses of sensory organs increase with increasing dose of stimuli

Question 10

What is the EC50?

Answer 10

The measure of the potency of a stimulus
Or the sensitivity of a receptor to it
The dose at which 50% of the maximal effect is reached

Question 11

What is the molecular basis of odour specificity in insects?

Answer 11

Thought they would be G proteins like vertebrates
Now know they are a novel type of ligand gated ion channels
7 transmembrane domain receptors (like g protein coupled receptors)
They are flipped in the membrane

Question 12

True or false

An insect olfactory receptor forms a tetramere

Answer 12

True

Question 13

True or false
Most odours are encoded as an activation pattern across receptors and some odours are encoded by the activity of a single type of receptor.

Answer 13

True

Question 14

Describe across fibre pattern coding

Answer 14

The message is coded in the pattern of activity across different sensory neurons

Question 15

Describe labeled line coding

Answer 15

The message is coded in the activity of a single type of sensory neuron

Question 16

What is bombykol used for?

Answer 16

Pheromone of the silk moth
Released into the wind
Another silk moth follows the scent

Question 17

What is male love dust?

Answer 17

Aphrodisiac that makes females receptive

Male flies above female and dusts it

Question 18

What are intraspecific phermones? (phermones are intraspecific)
What are interspecific allelochemicals? (allelochemicals are interspecific)

Answer 18

Act within species

Act between species

Question 19

What does semiochemicals mean?

Answer 19

Communication by chemicals

Question 20

There are 3 main types of allelochemicals 
Kairomones
Allomones
Synomones
Describe them

Answer 20

k = benefit the receiver, disadvantage the producer (host odours for tseste flies)
a = neutral to receiver, benefit producer (plant chemicals, deter feeding by insects)
s = benefit receiver and producer (flower odours attracting pollinators)

Question 21

What did Gottfried 2009 find?

Answer 21

Humans can turn a stimulus to a percept even if there are many volatile components, absence of some components, additional components or weak stimuli

Question 22

What is the approximate number of OR genes in
Mouse
Human
Drosophilia

Answer 22

1100
350
60

Question 23

What is pseudogenisation?

Answer 23

Mutations that render a gene non functional

Question 24

True or false

2-8% of Ors are psuedogenes with 50% of human V2Rs being psuedogenes

Answer 24

False
15-78%
All V2Rs

Question 25

Vertebrate ORs fall into 2 categories | What are these

Answer 25

``` Class 1 olfactory receptors (tuned to water soluble odorants) Class II (tuned to hydrophobic odours) Amphibians have both class 1 and class II In dolphins, Class II receptors have been psuedogenised - do not have class 1 ```

Question 26

Are vertebrate olfactory receptors G protein coupled receptors or novel type of ligand gated ion channels?

Answer 26

G protein coupled receptors

Question 27

Describe Linda Buck and Richard Axel's discovery of odour receptors

Answer 27

Dissected out olfactory epithelium Extracted RNA Reverse transcription to generate cDNA Used pairs of degenerate primers for GPCRs to amplify further candidate members of the GPCR superfamily olfactory epithelium Gel electrophoresis, look for banding pattern. Looked for multiple bands - all bands together added up to more of the expected length That indicated they amplified a family of different DNA strands - encode a family of different receptors - represents family of olfactory receptors

Question 28

Describe ORNs

Answer 28

Olfactory receptor neurones Each ORN has 8-20 non motile cilia The other end of the ORN has an unmyelinated axon 10-100 axons form into a bundle Each bundle becomes a primary olfactory nerve fibre The fibre passes through the cribriform plate The first synapse is in the olfactory bulb

Question 29

What is an odorant?

Answer 29

``` May be hydrophilic or hydrophobic Most are volatile (stimulus?) Dissolves in nasal mucous Diffuses to receptors on cilia Aided by odorant binding proteins (OBP) Clearance also aided by OBP ```

Question 30

Describe olfactory transduction

Answer 30

OBP and odorant bind Activate the receptor - 7TM-GPC It receives an appropriate ligand Undergoes a confirmational change Thereby activated g protein This activates adenyl cyclase Generates cAMP This cAMP acts on CNG-cation channels to open the channel Allows sodium and calcium to come into the cilia of the neuron Causes depolarisation The calcium causes further depolarisation by acting on calcium activated chloride channels Cl- leaves neurone and causes further depolarisation

Question 31

Why do we perceive taste?

Answer 31

Drives appetite Protects us from poison Taste for sugar - absolute requirement for carbohydrates Cravings for salt because we need sodium chloride in our diet

Question 32

Why do bitter and sour taste cause aversive, avoidance reactions?

Answer 32

Most poisons are bitter and as food decays, it goes acidic

Question 33

Why does umami drive our appetite for amino acids?

Answer 33

Meaty, savoury taste and we need proteins | Amino acids are the building block for proteins

Question 34

What are the 5 basic tastes?

Answer 34

``` Sweet Sour Bitter Salt Umami ```

Question 35

In mammals, taste buds are groups of 30-100 individual elongated cells - what are these cells called?

Answer 35

Neuroepithelial cells | Often embedded in papillae

Question 36

At the apex of the taste bud, microvillar processes protrude through a small opening called?

Answer 36

The taste pore | Below the taste bud apex, taste cells are joined by tight junctional complexes that prevent gaps between cells

Question 37

What 3 forms do the papillae come in?

Answer 37

Circumvallate Foliate Fungiform

Question 38

True or false | Different tastes are detected by different parts of the tongue

Answer 38

False | Spread out

Question 39

What are the two models that describe how taste buds are arranged?

Answer 39

Labeled line model | Access fibre model

Question 40

Describe the labeled line model

Answer 40

Sweet taste cell, bitter taste cell etc

Question 41

Describe the access fibre model

Answer 41

Each taste cell has a mixture of receptors eg sweet,bitter,salty

Question 42

Which model is most likely to describe how taste buds are arranged?

Answer 42

Labeled line model | Limited number of receptor kinds

Question 43

Describe the bitter receptor family - T2Rs

Answer 43

50-80 members Expressed in cells that also express alpha-gustducin (that is probably the g protein that is involved in the cascade of detecting bitterness) 70% of gustducin cells in circumvallate and foliate papillae express T2Rs

Question 44

Describe sweet and umami receptors

Answer 44

Heteromeric receptors made up of a combination of different subunits Coded for by a small gene family T1Rs All 3 T1R genes are expressed selectively in human taste receptor cells in the fungiform papillae This is consistent with their role in taste perception

Question 45

``` Sweet and umami receptors T1R1 + 3 = T1R2 + 3 = T1R3 on its own = Umami is possibly mediated by both what and what receptors? ```

Answer 45

amino acid receptor = umami sweet receptor may be the sweetener receptor mGluR4 and T1R1+3 receptors

Question 46

Fat CD36 is an integral membrane protein on cell surface. What does it do?

Answer 46

Binds fats | Has a role in fatty acid metabolism, taste and dietary fat processing in the intestine

Question 47

Lingual lipase reduces triglycerides to what?

Answer 47

mono and di-glycerides and free fatty acids (FFA)

Question 48

What do FFAs do?

Answer 48

Free fatty acids | Inhibit delayed-rectifier channels in taste cells

Question 49

What is astringency taste?

Answer 49

Unripe fruit tastes, tannins and oxalic acid Tannic acid produced as a defense against insects - activates specific neurones in the brain This suggests it could be considered a separate flavour/taste

Question 50

What is metallic taste?

Answer 50

eg Cu2+, FeSO4 or blood in mouth Some drugs can cause this taste eg metronizadole, acetazolmadide