The five major senses--smell, taste, vision, hearing and touch--are described in this chapter.
All rely on mechanisms involved in transduction of other signals.
Hearing and touch have different structures but have the same ankyrin repeats.
There are hundreds of different odorant re ceptors in the human genome.
When an odorant arrives with the right shape to bind, a Gprotein binding to GTP and triggering adenylate cyclase.
The stimuli send signals to areas of the brain, and the perception appears to be decoded by a combinatorial mechanism.
A scent may be the result of a dozen ORs firing at the same time.
It appears that all of the signals converge on a single area of the brain, so that many different molecule can cause the same bitter signal.
Glucose and other sugars cause a similar process for sweet and salty taste.
Ion channels have salty and sour tastes.
Rhodopsin is a 7TM receptor that is bound at the cen ter.
The shape of the eye when light isomerizes it is the same as it is when other 7TM receptors bind to their ligands.
The result inside the cell is the same as the result inside the cell outside.
The cone photoreceptors are very similar to rhodopsin and are able to see color in the red, green, and blue regions.
Heterogeneity of the photoreceptor genes causes color blindness.
Hearing and touch use similar systems.
Nerves are stimulated by opening ion channels when hair cells in the cochlea are Displacement of hair cells in the cochlea causes Nerves are stimulated by opening ion channels when hair cells in the cochlea are
Touch seems to use the same receptors for touch, temperature and pain.
The active compound in hot peppers is Capsaicin.
It appears to be an ion channel and involved in detecting pain.
There is a discussion of the magnetic sense.
What happens when an OR binding to an odorant?
The figures on page 360 of the text show the potassium channel and the sodium chan nel.
Discuss how rod cells recover after being stimulated by light.
The structures of R- and S-carvone are presented at the start of Section 32.
One smells like spearmint and the other like caraway seeds.
The structures of tetrodotoxin and amiloride are compared.
The rod cell has two main regions in the left column and one in the right column.
The events should be placed in the correct sequence.
The text states that a likely ortholog of the transduction channel used in human hearing has been found in fruit flies.
Birds use the Earth's magnetic field to migrate.
There are 260 functional genes.
If the human genome has 40,000 genes, one can either calculate the percentage of functional genes or the percentage of "apparent" genes.
The yield is 750/40,000.
This chunk of the genome shows how important the sense of smell is in higher animals.
In three dimensions they would bind to an active site differently than they would on paper.
They smell completely different because they interact with different ORs.
The OR receptors are found everywhere.
If the genes can be made from cells in the nose, that means that the genes could be an OR.
When a scent is triggered by a single chemical, there will be an array of receptors that perceive it, and the sensation will be decoded by a process called a combinatorial process.
Both contain the guanidinium moiety.
The rest of the molecule will block the channel if this cation is attracted to sodium chan nels.
The large yellow portion is missing in the brain and has a lower affinity for Glu in the umami receptors.
The form of transducin that is activated is called transducin.
The closing of the channels is caused by the hydrolyzing of cGMP to 5'-GMP.
The return to the dark state requires the deactivation of both cGMP and photoexcited rhodopsin.
Transducin is returned to the inactive state by the hydrolysis of GTP bound to Ta.
The photoexcited rhodopsin is activated by the rhodopsin kinase.
The binding of transducin is blocked by the phosphorylated rhodopsin.
The synthesis of cGMP is made by nanylate cyclase.
Light-induced lowering of Ca2+ reactivates the formation of cGMP.
Chickens have a violet color so the answer would be (b) only.
There are two genes on the X chromosome that are red and green.
Women have two chances to get it right because they have two copies of X.
Men are only given one chance because they are XY.
Many X chromosomes have a missing visual pigment genes.
Gene duplication leads to orthologs that differ in function.
Paralogs are similar in function to different species.
Both flies and humans use the same molecule in the air.
Making magnetic "hats" would be one way to see if the birds can be made to fly on their normal routes.
Birds use the magnetic field as a kind of calibration, so this may not work.
The inability to smell musk is a very common specific anosmia.
Some 10% of the population smell nothing when exposed to the pure compound, and another 20% find the smell unpleasant.
This means that the cork has caused the wine to have trichloro-anisole in it.
The compound ruins the wine, making it smell like wet cardboard.
Some wine lovers report that as much as 20% of the bottles they open are corked.
You should consider the bitter receptor in your answer.
acidic foods taste better after they have been chewed.
A lemon is good, and a tomato is good.
The mechanism of the active substance has not been discovered.
There is a close relative of the brain's NMDA receptor.
The central nervous system has several glutamate receptors.
Police investigated a car that was pulled over on the side of the road.
The driver stated that he had seen streams of blue light coming out of his dashboard.
The officers thought the man had taken hallucinogenic drugs, but he told them he had takenViagra earlier in the evening.
You can give the reason for your choice.
A color vision pigment that absorbs red light is cleaved to separate it from the reti nal.
The same thing is done for a blue light absorber.
The opsin from the blue-absorbing pigment is used to create a new pigment.
Cochlear implants have helped many people who are hard of hearing.
Zostrix contains a substance called capsaicin.
Rubbing the cream on the less sensitive parts of the body can provide relief from neuralgia or arthritis pain.
The hot principle of the chili pepper can cause burning of mucus in the eyes, nose, and mouth, so avoid them.
The answer to this question is not in the textbook, so you will need to search the internet or literature to find it.
The 10% who are anosmic for Musk have either a deficiency or a change in specificity.
People who can smell the scent usually describe it as sweet and floral.
It smells like old wet newspapers or something stored in the attic for too long for 20% of people who dislike it.
The ability to bind to musk seems to have been developed by a different receptor.
The structure of natural Musk is interesting.
The old saying "de gustibus non disputandem est" means "to each his own taste" if one appreciates the sensory differences these genetic variations cause in humans.
There are many people with a specific anosmia.
This can lead to a diminished ability to smell it.
The unlucky people who smell it often find that they can't drink their expensive wine because of a cheap little cork.
Plastic corks or screw-on caps are the obvious solution.
Some people believe that the gentle oxidation that occurs through a cork allows the wine to age better.
The advantages of real corks are overstated by others.
Losing an OR leads to the inability to smell it.
The perception of bitter tastes is unaffected by the loss of one kind of bitter receptor.
All of the many receptors send their signals to the same area of the brain, so nothing is lost when one or two of them lose function.
Some people think that the protein stimulates the sweet receptors when exposed to acid.
It is possible that it is a glycoprotein and that some sugar hydrolyzes off in the presence of acid.
The compound has been proposed as an aid to people who are trying to lose weight.
Similar changes in the taste of other foods can be found in Artichokes.
It's not the preferred transmitter for the NMDA receptor.
The ability of that receptor to bind and respond to the artificial compound is what distinguishes it.
Viagra's mechanism of action is based on its ability to block PDE-5.
It prevents cGMP from being cleaved.
If the levels of the drug are high enough, the PDE6 in the retina becomes resistant to cycling, so that normal cycling can't happen.
Some people have blue-tinted or blurry vision, sometimes with more extreme manifestations.
Scientists are working on Viagra-like drugs that are more specific for PDE-5 and not stimulating the retina as much.
There are long sequences of alternating sin gle and double bonds in compounds that absorb visible light.
The visible range of the spectrum would have negligible absorbance with compound B unconjugated.
The absorbance in the visible range is significant.
The blue end of the spectrum is reflected by the red light absorbed by the pigment.
The cycle of visual stimulation could not happen because of this.
The blue light will be absorbed by the new pigment.
All color pig ments have the same vision.
The absorption maxima varies among the pigments.
It was possible to mimic the kind of nerve signals generated by the cochlea.
If enough nerves are present in the inner ear to convey the signals, an external device will transduce them into electrical signals just like the hair cells in the cochlea.
The brain's electrical impulses are the same as those experienced by a hearing person.
The pain is not felt when capsaicin is rubbed on a knee or elbow.
The response to pain on the surface of the skin appears to be flattened by the amount of capsaicin applied.
There is less response to real pain under the skin.
Near the end of the article, pheromones are discussed.
The fact that women living in the same dormitory will have the same menstrual cycles is circumstantial.
There has yet to be a demonstration of human pheromones.
Isoleucine is one carbon larger than valine.
Heptanal has the same geometry and is one carbon smaller.
There is a chance that these two features compensate at the active site.
The extra carbon on Ile-206 could interfere with the binding of the shorter heptanal.
The AWB neurons havereceptors that induce avoidance behavior.
It would be expected that the general behavior would remain the same.
The two compounds that must be present are C5-COOH and HOOC-C7 COOH.
The pattern of non-activated receptors makes it impossible for other compounds to be present.
The potential for very rapid time resolution is due to the direct action of hydrogen ion or sodium ion on channels.
Second messengers will exhibit slower time resolution when they respond to bitter and sweet tastes.
The difference in arrival time for the human hearing system is about 2 x 10-5 s. A system that uses 7TM receptors and G proteins would be too slow because it would need a response time of at least several milliseconds.
The olfactory response would be completely eliminated.
If adenylate cyclase was always active, there wouldn't be an opportunity to increase the concentration of cAMP in the olfactory system.
There were no signals that could be processed.
It would be more difficult to reduce the level of the drug in the visual system if it was always active.
The signal amplification would be impaired.
The rate of synthesis would no longer be sensitive to calcium, which would affect the visual recovery.
The tastant would be sweet because the rodents preferred the water with the added tastant.
There are many examples of mimicry in the biological world.
The plant may be able to decrease the extent to which it is eaten by animals if it is given a bitter taste.
It's a precautionary measure for airline safety.
The pilot's response to an emergency situation could be affected by the inhibition of a cGMP phosphodi esterase that is prevalent in smooth muscle.
It is necessary for all senses to generate and maintain ion gradients.
It is necessary for the synthesis of cAMP.
The action of gustducin is required for the detection of bitter and sweet tastes.
GTP is required for the action of transducin.
Hearing and touch, the ability to generate and maintain ion gradients and membrane potential may be required for other roles as well.