Tuesday, March 29, 2011
Smells Good
Chapter 8 of Neil Shubin's book talks about how scents are created, through connections with your brain. He explains that a 'lock-and-key' mechanism is used for smelling, with molecules that connect to receptors in your nose, which send signals to your brain. How does this 'lock-and-key' system work and how does it relate to other topics we've learned previously in the school year? Why is this mechanism necessary for certain functions to work properly? How would these functions be different without this mechanism? Explain using Shubin's knowledge, Campbell, or other sources.
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The lock-and-key model is very important in that it allows for a level of specificity, an aspect that is vital to almost any cell function--that is, this model guarantees that only specific molecules or substances can bind to the receptor and allow for the particular process to continue, which, in this case, is the sending of signals to the brain for certain odors, which may stimulate activity in other parts of the body, depending on what the substance that is binding to the receptor. This concept relates to an area we learned earlier this year--enzymes. Enzymes have a specific active site, to which only certain substrate(s) can bind to. Though there may only be one substrate which can fit into one active site, oftentimes there are a few different substrates that may fit into the active site (induced fit model); the shape of the substrate also often changes slightly as it binds to the active site. Enzymes may also have an allosteric site, where a substrate may bind and change the shape of the enzyme, to either inhibit or stimulate the binding of substrate to the active site. Once the substrate has bonded, it is then broken down or modified by the enzyme into the product, which is then released; enzymes are not used up in the reaction. Without lock-and-key specificity, it would be more difficult for our odor molecules to distinguish between different odors. Thus, since there would not be a multitude of different receptors that specific molecules would bind to, different scents may be incorrectly perceived as the same scent, and signals may become more mixed as they are sent to the brain. Consequently, this lock-and-key receptor model of our nose is vital to its function, especially when an odor may "involve lots of molecules, and, accordingly, lots of receptors sending signals to our brains" (Shubin 141) because since each receptor goes with a specific molecule, it allows for a simpler distinction between different scents, and thus more clear identification of odor and of which signals should be sent to the brain.
ReplyDeleteKathy Li, kathy2132@gmail.com
Sources:
Campbell & Reece
Your Inner Fish
http://www.elmhurst.edu/~chm/vchembook/571lockkey.html
As Kathy mentioned, the lock and key model of the smell receptors is also seen in enzymes. When a molecule enters the nose, it binds itself to a receptor with a similar shape, like what happens in the lock and key model. This stimulates the olfactory receptors, which are located in the olfactory epithelium which contains about 20 million nerve endings, create a difference in membrane potential, after which the scent in categorized, sent to the hypothalumus, thalumus, and pituitary gland, and a response to the scent occurs (us being aware of the scent.) A slightly similar pathway with many psychoactive drugs such as nicotine. After nicotine enters the body and bloodstream and encounters a neuron. The small nicotine molecules act as a neurotransmitter. However the body does not contain receptors for nicotine molecules. It does however, contain the very similar in shape, acetylcholine receptors. The nicotine is able to bind to these receptors much in the same way that CO is able to bind to hemoglobin instead of O2. This is a process known as competitive inhibition. Acetylcholine receptors are meant to stimulate the cardiovascular and muscular system. Thus when the nicotine "neurotransmitters" bind to the acetycholine receptors on the dendrites they stimulate the cardiovascular, respiratory, and muscular system which is why a smoker's heart beats faster and metabolize nutrients after having a cigarrette.
ReplyDeleteSources: http://health.howstuffworks.com/wellness/drugs-alcohol/nicotine4.htm
http://www.diy-stress-relief.com/smell.html
http://health.howstuffworks.com/human-body/systems/nose-throat/smell2.htm
Campbell&Reece
Everything that Kathy said was completely right. I would just like to add on a little bit more detail as to how the process of smelling actually works. It begins when airborne molecules stimulate the olfactory epithelium which is roughly one square inch of surface area within your nose. Mucus, secreted by the olfactory gland, coats the epithelium’s surface and aids in the dissolving of odorants. The receptor cells are neurons with knob-shaped tips called dendrites. The dendrites are covered with olfactory hairs that bind with odorants and then send an electrical impulse to the olfactory bulb through the axon at its base. The pulse then travels to the brain where it is interpreted as a sense.
ReplyDeletehttp://health.howstuffworks.com/human-body/systems/nose-throat/smell2.htm
How the body interprets the smell is completely another story. But luckily, it has been deciphered for the most part using molecular techniques. In 2004, Richard Axel and Linda Buck won the Nobel Peace Prize for their work in Physiology and Medicine because of their discovery of a large gene family (about 1,000 different genes) that produced roughly 1,000 olfactory receptor types. This shows that each olfactory cell has only one type of odorant receptor which explains why some people cannot smell certain smells. Because of this, our olfactory cells are highly specialized for a few odors. These olfactory cells send nerve impulses through micro domains, glomeruli, through the primary olfactory area, and into other parts of the brain where the impulses form a pattern which is then interpreted by those sections of the brain into our perception of a smell.
Axel and Buck also cloned olfactory receptors to show that they belonged to the family of G protein coupled receptors. These receptors are activated by light-sensitive compounds, odors, pheromones, hormones, and neurotransmitters, and can vary in size from small molecules to peptides to large proteins. They are also the target of approximately 30% of all modern medicinal drugs.
http://nobelprize.org/nobel_prizes/medicine/laureates/2004/press.html
Matt Micucci (coochqbk@sbcglobal.net)