Archive for the ‘light’ Category
Eat Your Carrots! The Chemistry of Vision
“Sandwich Carrots-Dainty Sandwich Carrots.” Hand-colored etching. Gillray, James, 1756-1815, engraver. Published by H. Humphrey, 1796 Dec 3d, London.
Image courtesy of Library of Congress.
You’ve probably heard the old adage about eating carrots for good vision. Well, there is some truth to it. Carrots contain a high concentration of β-carotene which gets broken down in the intestines to form the aldehyde (hydrocarbon) form of vitamin A, cis-retinal. Vision deteriorates in the absence of vitamin A because cis-retinal is trafficked along the protein, opsin, to produce electrochemical signals from light.
Our retinas perceive light in tiny particles called photons. As soon as these photons hit the retina, they isomerize cis-retinal to trans-retinal. Trans-retinal then bonds to opsin to form rhodopsin. Rhodopsin is a purple pigment in the photoreceptor cells of the retina that reads blue-green light. This is the first step of the phototransduction cycle where photon energy is transferred to a series of signaling and diffusing protein complexes.
Retinal isomerism drawn with ChemDraw
Mutated forms of rhodopsin will be folded and transported differently and could lead to deteriorated vision or blindness. In more rare cases, mutations can cause rhodopsin to be constantly activated, even in the absence of light. Hypersensitivity, autoimmune disorders, and mutations can all cause rod cells in the retina to undergo apoptosis or cellular self-destruction. This sort of degradation of the retina will ultimately lead to deteriorated vision and eventually blindness.
The absorbance of cis-retinal is optimized at approximately 100 nanometers less than rhodopsin and it is a very rigid molecule because of the arrangement of its double bonds. Thanks to isomerism, we can see in color as opposed to ultraviolet! As all of the above demonstrates, our ability to see involves a series of complicated and precisely regulated bio-chemical processes, and carrots play their role.
We will be exploring more about vision loss and blindness in the upcoming GLIMPSE issue 10, Blindness. In the meantime, let us know your thoughts, research, questions, or experiences related to the topic.
If you’re interested in the chemistry of vision and why we perceive the section of the electromagnetic spectrum that we do, you might also be interested in GLIMPSE, issue 4, Color, and the article on “Human Potential for Tetrachromacy” by Kimberley A. Jameson and the online supplementary article.
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Myya McGregory is the GLIMPSE 2012 Science Writing Intern. She is a junior double-majoring in chemistry and economics at Williams College. She enjoys music, dance, and literature.
Study Imaging Science at MIT for $0 a day
Digital refocusing is a computational photography technique that allows one to change the focus point in an image after capture, using additional data collected through camera enhancements such as a coded aperture mask. (Image by Prof. Ramesh Raskar.)
September’s here, and it’s time to put the thinking cap back on. No need to enroll or pay tuition…or to do homework. Official students, garage tinkerers, lifelong learners, and the generally curious can learn about the latest in imaging technology from the MIT Professor Ramesh Raskar. Now available via MIT’s (visionary) Open Courseware site:
“Computational Camera and Photography” http://ocw.mit.edu/courses/media-arts-and-sciences/mas-531-computational-camera-and-photography-fall-2009
Thanks, Massachusetts Institute of Technology and Professor Raskar, for sharing your knowledge with everyone that’s interested!
Check out more DIY MIT courses here:
Hmmmm… imaging technology not your thing?
How about:
“Film as Visual and Literary Mythmaking?”
Or
“Laboratory in Visual Cognition?”
Or….
Mama Don’t Take My Polaroid Away
Much like the American singer/songwriter Paul Simon who crooned nostalgic over visual technology in his 1970s hit “Kodachrome,” Austrian entrepreneur Florian Kaps is making his own case for keeping the Polaroid camera alive in today’s visual market.
Wall Street Journal writer Eric Felten in “It’s Baaaaack! But Polaroid Film Was Just Lucky” describes Kaps’ tenacious journey to save the Polaroid from utter oblivion—from begging the junk men not to destroy the last functioning Polaroid factory machines outside of Amsterdam while he vigorously raised money to save them, to putting together a team of scientists to come up with a new sepia-toned black-and-white film that could be used in standard Polaroid cameras (the arcane chemicals originally used to run in the machines could no longer be produced).
What’s resulted from Kaps’ valiant efforts to preserve a medium that we often associate with the psychedelic, saturated ’60s (although it was invented in 1929) is The Impossible Project. It’s a website that allows individuals around the world to peruse and purchase classic Polaroid cameras with modern twists, and also a wide variety of analog instant film.
The Glimpse team gives kudos to Kaps for preserving a nearly extinct perspective, and for keeping the dialogue between new and old visual technology alive and well.
Above image titled “Enschede5.” ©The Impossible Project
Finding the stars through the light pollution
Courtesy of C. Mayhew & R. Simmon (NASA/GSFC), NOAA/ NGDC, DMSP Digital Archive
It’s a breathtaking sight, looking down at a glowing Earth. An ominous one, too.
For those of us living inside the glow who can only look upward, the brilliant stars are becoming less so. They’re fading behind streetlights and porchlights and lamplights and headlights. And in Glimpse‘s forthcoming Cosmos issue, Scott Kardel wants them back.
Kardel spends his days (and starry nights) at Palomar Observatory, where astronomers dodge terrestrial lights to capture cosmic ones. Stay tuned for “Dimming the Lights” in March 2010 for reasons why not to be scared of the dark.
(The Cosmos issue scheduled for blastoff! in 5..4…3…)
From Our Internal Organs to the Cosmos
Congratulations to this year’s Nobel prize in physics recipients!
On Tuesday Oct. 6, 2009 at 11:45 am, the recipients of the 2009 Nobel Prize in Physics were announced at The Royal Swedish Academy of Sciences in Stockholm. One half of the prize was awarded to Charles K. Kao for his research in glass fiber optics, and the other half of the prize was evenly divided between Willard S. Boyle and George E. Smith for their invention of the charge-coupled device, or CCD.
In 1966 with his college George A. Hockham at Standard Telecommunication Laboratories, Kao proposed a solution for the then thought implausible transmission of long range information technology. They suggested that impure glass particles inhibited long range light transmissions in optical fibers. By chemically purifying the glass with fused quartz and fused silica, Kao purposed a method of extracting an ultra-thin fiber thread that would carry at least 1% of light over the distance of 1 kilometer. Today this glass fiber optics technology is fused with our everyday lives and employed in various forms (like the internet), allowing for instantaneous transnational and global cable communication.
In 1969, Willard S. Boyle and George E. Smith of Bell Laboratories discovered the CCD while drafting the proposal for a technological information storage device. What they came up with instead was a light transmission technology, a digital image sensor, based on Albert Einstein’s theory of the photoelectric effect. When particles of light enter the light sensitive silicone plates, the CCD, electrons in the photocells emit at equal proportions as the incoming light, transferring the incoming optical image into a digital one in the form of pixels; opening the door for even more novel inventions like pixelated digicams, 96 megapixel images of outer planets on the Hubble telescope, and internet porn. The image above is of a star formation called the Orion Nebula. It was taken by the Advanced Camera for Surveys (ACS) on NASA’s Hubble Space Telescope in 2006.
For more information about the 2009 Nobel laureates visit the Nobel prize website.
