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An ‘Amazing Race’ of the Senses April 29, 2011

Posted by abueno526 in Biology, Fun, Physiology.
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The last team to check in may be eliminated…

The Amazing Race is a reality tv show in which pairs of contestants race around the world in a challenge of wits, strengths, and abilities to try to ultimately come in first place and win the coveted million dollar prize and of course, bragging rights.  Throughout its 18 seasons in the United States, contestants have been put through a wide array of challenges, including participating in an acrobatic act, carrying furniture and grains across the city, and identifying a correct tune being played in a sea of pianos.

Tea anyone?

In a specific episode this season, the contestants were required to drink a cup of papaya mango tea in a small shop in China. Later on that day, they had to pick out that same flavor of tea from a table of hundreds and hundreds of different cups of tea by recognizing the smell and taste. Although a daunting task, all of the teams successfully completed the challenge by identifying the tea.  But, with so many scents and flavors on the table, how were they able to identify the correct cup?

Olfaction – Odorants

All things considered, humans have the ability to recognize and distinguish 7,000 to 10,000 different smells.  But how is this possible?  The first thing to consider is the human capability to detect odorants, which are typically small organic molecules with some amount of volatility so they can be carried in a vapor from to the nose.  These small odorant molecules are actually detected by their shape, not from any other physical properties that they exhibit.  This means that the different smells come from the way the molecule interacts with the binding site it is associated with.  A common example to better explain this idea can be seen in the molecule carvone (depicted left), which has distinct R and S configurations.  Although the two are mirror images of one another, the R conformation has a scent of spearmint, while the S configuration of caraway, indicating their difference in binding.

Olfaction – Odorant Receptors

Scents are detected in the main olfactory epithelium  of the nose, and are are identified by one of the million sensory neurons that dwell there, which all contain cilia with receptors.  Although we are able to recognize upward of 7,000 distinct scents, humans only have 350 odorant receptors  As seen in the picture to the right,molecules bind to the receptors that are on the cilia, nerve impulses are generated from the binding and travel through the neurons, and finally move to the olfactory bulb.  Throughout this process (binding to olfactory bulb response), cAMP and GTP levels in the body increase, meaning that the process uses 7TM receptors.  These compounds are released in a cascade process, depicted to the left.  When the odorant binds to the receptor, a G protein is activated and binds to

GTP.  This complex then moves to activate an adenylate cyclase, which increases cAMP levels.  High cAMP levels activate and open ion channels, which creates an action potential and allows the smell of an odor to come through.

Olfaction – Scent Recognition

But with only 350 distinct receptors, how are we able to detect thousands of smells?  The answer lies in the fact that most smells are composed of several odorant receptors, which can be activated at different levels of odorant.  In other words, there is not a one to one relationship for odorant to receptor, but instead odorants can activate multiple receptors and receptors can be activated by multiple odorants.  As an example, the odorant C6COOH activates six different receptors, while C5OH, C6OH, and C7OH all activate the same receptor.

Olfaction gone awry 

Sometimes, we are unable to detect some scents, called a specific anosmia.  although everything seems to be functioning normally, certain compounds are not detected by these individuals, indicating that it it a genetic inheritance of a mutation.  Although over 80 have been identified, some examples of molecules that are unable to be smelled include isobutyric acid, which is responsible for the  smell of sweat, and n-Butyl mercaptan, the smell that skunks give off.

Gustation – An Overview

The tongue has the ability to recognize 5 major tastes in the mouth: bitter, sweet, salty,sour, and umami (savory).  A diagram of where these individual taste buds are located can be found to the right, excluding the umami taste.  “Umami” is a word derived from the Japanese language, and includes the tastes of glutamate and aspartate.  Much less is known about this taste than the others because this “savory” flavor has only been distinguished from the others within

the past five to seven years.  Receptors for tastants are more commonly referred to as taste buds, which are made up of about 150 cells.  Microvilli on the surface of the tongue bind to tastants and send an impulse through the sensory neurons to the brain to identify the specific taste.  The tastes use different methods to detect the taste, all of which are outlined below.

Gustation – Salty and Sour

Salty and sour tastes opperate in a similar manner in the fact that they both utilize ion channel interactions.  In the case of salty flavors, this is done through sodium ion and their corresponding amiloride sensitive Na+ channels.  Sodium ions pass through the channels on the front of the tongue creating a current, amiloride attempts to block this current, and a salty flavor can be tasted.  Similarly, the sour taste acts through a hydrogen ion channel .  Hydrogen ions flow through the pores on the sides of the tongue, and a sour taste is observed.

Gustation – Sweet and Bitter 

Unlike the salty and sour tastes, both the sweet and bitter receptors utilize a 7TM receptor complex, as mentioned above in the olfaction discussion.  Because of this, they respond to a larger range of stimulants.  Sweet receptors typically respond to glucose, sucrose, aspartame, saccharine, and even some proteins.  While being researched, scientists discovered that these compounds interact with the T1R1, T1R2, and T1R3 receptors in different combinations with one another.  They all pick of variations of sweetness, with the T1R2 and T1R3 receptor being the most sensitive to the sugary taste and the T1R1 receptor by itself being the least sensitive to the taste.  The bitter receptor acts in a similar manner, however, its receptors respond to toxic alkaloids.  TR2 receptors are responsible for this taste, which is typically recognized at the back of the tongue.  In this regard, it should be noted that taste receptors are much less selective than the scent receptors due to sheer number (350 vs. 5).  For example, in the case of the bitter taste, we usually recognize just bitter in general and are unable to distinguish one bitter compound from another.

Gustation – Umami 

The final taste is umami, which is recognized as the savory flavoring and utilizes 7TM receptors as well.  These receptors respond to glutamete, aspartate, and even MSG.  It is similar to the sweet receptor in the fact that it utilizes the T1R3 receptor, but it is also paired with the T1R1 receptor.  Unlike the sweet receptor that may utilize different combinations of the receptor, the savory flavor can only be obtained with activation of both the T1R3 and T1R1 receptors simultaneously.

A Complimentary Combination 

So, through a combination of the senses, contestants were able to identify the correct cup of tea.  Using the odorant receptors to bind to the scent molecules and the specific taste buds on the tongue to identify the tastes, it is possible to identify a particular item in a sea of many.  As a tip for the contestants for next time, they may want to rely on their nose more than taste due to the high specificity of the olfaction system!

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Survivor? Or Starvation? March 4, 2011

Posted by abueno526 in Biology, Chemistry, Nutrition.
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Outwit. Outplay. Outlast.

Survivor. A show with the motto above,  “Outwit, Outplay, Outlast.” Contestants are put on a deserted island with meager food, shelter, and comforts to compete in a series of challenges as they try to become the ‘Sole Survivor”.  Although the glory of winning the title is great, what is physically happening to contestants’ bodies as they put themselves under these extreme conditions?  Some, like Russell Swan from Survivor:Samoa, get fatigued earlier than others, having to be removed from the game for medical reasons.  When this shut down occurs, what is happening?  How far can they really be pushed until they move into a starvation-like mode?

How does it all start?

Typically, glucose is the major energy provider to the body.  Fats can be a precursor to glucose, and ample amounts of them in the body lead to proper function and metabolism.  When one is in starvation mode, the liver is the first to sense this.  Because the body is unable to convert fats into glucose, it biochemically makes a shift to harness more of its energy from ketone bodies in order to save the muscles from deterioration via protein breakdown.

And the downward spiral begins

This switch to the use of ketone bodies is also vital to supplying energy to the brain cells, which is a top metabolic focus for the body no matter its state. In this protection mode, and use of a new fuel source by the brain, blood glucose levels drop dramatically.  This way of living will continue until all fatty acid energy stores have been used up.  Metabolic function will switch from using ketone bodies to its last

resort of proteins for energy.  Final stages of starvation such as these can result in heart arrhythmia, liver failure , and a discontinuation of muscle functioning, ultimately leading to death.

What would you do for a million dollars?

So, when a Sole Survivor is picked at the end of 39 days, what sort of condition are they in?  Although perhaps a few sizes smaller, the contestants will not have reached a true starvation mode due to the time frame of the show and availability of some food for nourishment.  Although they can do it, it’s definitely not recommended unless you’re playing for the million dollar prize!