The Chemistry of Vision April 17, 2008 Andrew Isleib Eric Sterne Jonathan Arnold Min Eun Lee Samara Shiromani
Jun 03, 2015
The Chemistry of VisionApril 17, 2008
Andrew Isleib
Eric Sterne
Jonathan Arnold
Min Eun Lee
Samara Shiromani
Agenda
• Introduction: Retinol and Eye Biology
• Chemistry of photoreception
• Color Vision and Color Blindness
• Macular Degeneration
• Concluding Remarks
• References
Introduction
• Conjugated systems - Dr. Phillips presented -Carotene and retinol
• We will explain retinol’s role in vision and problems with vision– Retinal - Aldehyde form of Retinol
Introduction: Sources of Vitamin A (Retinol)
• Humans cannot synthesize retinol from scratch– Must ingest it directly or one of its precursors
• Animal sources of preformed vitamin A– Liver, Milk, Butter, Cheese, Egg Yolk
• Provitamin A Carotenoids - convertible into vitamin A in body– Beta-Carotene: Carrots, Spinich, Kale, Collard
Greens, Sweet Potatoes, Pumpkin, Cantaloupe– Lutein and Zeaxanthin
Introduction: The Eye
Photoreception takes place in Rod and Cone cells of the retina
Retina
Rod Cells
Cone Cell
- Opsin : Transmembrane G-Protein receptor
- Retinal: Chromaphore responsible for visible light absorption
- Retinal + Opsin = Rhodopsin
Introduction: Rhodopsin
Introduction: Phototransduction
A photon is absorbed by Rhodopsin which causes a conformational change in retinal
11-Cis Retinal
Introduction: Phototransduction
The conformational change allows a G-protein to replace GDP with GTP - initiates transduction pathway.
“All-Trans” Retinal
Chemistry: Retinal Binding
• Mechanism of Schiff Base (Imine) formation– Lysine side chain ends in -NH2
Chemistry: Rhodopsin Absorption • Positive charge distributed
over conjugated -bond system– Stabilized by amino acid
environment– Narrows distance between
HOMO and LUMO: Red Shift
• Entire photon must be absorbed– Lower energy - Longer
wavelength
MO
En
erg
y
HOMO
LUMO
HOMO
LUMO
Retinal Rhodopsinmax=370nm
max=498nm
MO
En
erg
y
Color Vision: Cone Cells
Color Vision
• Trichromatic Vision: Red, Green Blue
Ishihara TestWhat numbers do you see?
Color Blindness• Missing or defective pigment proteins for
certain cone cell types– ~8% of men, rare in women– X chromosome codes for cones
• Types of Color Blindness– Achromatopsia - black and white vision– Dichromacy - 2 functioning cone types– Anomalous Trichromacy - shifted cone absorption
• Non-Genetic Causes– Disease, Accidents, Medication
Losing the LightIntroduction to Age-Related Macular Degeneration
Normal Retina
Retina with AMD
Progression of AMD
Chemistry:A2E-epoxides
• A2E: autofluorescent pigment– Pyridinium polar head group– Two hydrophobic retinoid tails
• With light A2E creates epoxides at its C=C double bonds
• A2E-epoxides damage DNA– DNA Lesions, Altered gene expression
– Potential link to AMD
• Vitamin E and C reduce A2E-epoxide
Conclusion
• Improved understanding of how we see?• Just found out you are color blind?
– Support Group: http://dailystrength.org/c/Color-Blindness/support-group
• Age Related Macular Degeneration– Antioxidants: protect your vision as you age
• See Better: keep up your supply of retinol– Eat your carrots, greens, liver, etc.
References
• Shichi, Hitoshi. Biochemistry of Vision. New York: Academic Press, 1983.• Chang, Raymond. Physical Chemistry for the Biosciences. Sausalito, California:
United Science Books, 2005.• Lugtenburg, Johan, Muradin-Szweykowska, Maria, Heeremans, Carola, and
Pardoen, Johannes A. “Mechanism for the opsin shift of retinal's absorption in bacteriorhodopsin.” J. Am. Chem. Soc., 108, 11, 3104 - 3105, 1986, 10.1021/ja00271a050.
• Wachtler, T. Doi, E., Lee, T.-W., & Sejnowski, T.J. (2007). "Cone selectivity derived from the responses of the retinal cone mosaic to natural scenes. Journal of Vision, 7(8):6, 1-14. <http://www.journalofvision.org/7/8/6/>, doi:10.1167/7.8.6.
• Casidy, Rachel and Regina Frey. “’I Have Seen the Light!’: Vision and Light-Induced Molecular Changes.” Department of Chemistry. 2000. Washington University. 25 Mar 2008, <http://www.chemistry.wustl.edu/~edudev/LabTutorials/Vision/Vision.html>.
• Ishihara Test for Color Blindness. <http://www.toledo-bend.com/colorblind.Ishihara.html>
References
• Ophartd, Charles, E. “Chemistry of Vision.” 2003. Elmhurst College. 15 Mar 2008. <http://www.elmhurst.edu/~chm/vchembook/531vision.html>.
• Ophartd, Charles, E. “Beta-Carotene and Vitamin A.” 2003. Elmhurst College. 15 Mar 2008. <http://www.elmhurst.edu/~chm/vchembook/532vitaminA.html>
• Dutton, Frank. “Ishihara Test for Color Blindness.” 2 Apr 2008. <http://www.toledo-bend.com/colorblind/Ishihara.html>
• Sparrow, Janet R., Heidi R. Vollmer-Snarr, Jilin Zhou, Young P. Jang, Steffen Jockusch, Yasuhiro Itagaki, and Koji Nakanishi. “A2E-epoxides Damage DNA in Retinal Pigment Epithelial Cells: Vitamin E and Other Antioxidants Inhibit A2E-Epoxide Formation.” The Journal of Biological Chemistry. Vol. 278, No. 20, Issue of May 16, pp. 18207–18213, 2003.
• Wade, L. G. Jr. Organic Chemistry. Sixth Edition, New Jersey: Pearson Prentice Hall, 2006
• Yamadaa, A. T. Kakitania, S. Yamamotob and T. Yamato. “A computational study on the stability of the protonated Schiff base of retinal in rhodopsin.” Chemical Physical Letters, Vol. 366, Issues 5-6, 20 December, pp. 670-675, 2002
References
• Nolan, Donia, E. “Normal Age Related Vision Loss and Related Services for the Elderly.” 2002. Stephen F. Austin State University. 20 Mar. 2008. <http://hubel.sfasu.edu/research/donia/aging_visual_changes.htm>
• Bowmaker J.K. and Dartnall H.J.A., "Visual pigments of rods and cones in a human retina." J. Physiol. 298: pp501-511 (1980).
• “Sensory Systems.” 2006. Bellarmine University Department of Biology. 2 Apr. 2008. <http://cas.bellarmine.edu/tietjen/HumanBioogy/sensory_systems.htm>
• Gill, Cynthia. “Web Page for Bio 416L.” 2007. Hampshire College. 2 Apr. 2008 <http://helios.hampshire.edu/~cjgNS/sputtbug/416l/HumanPhys.html>
• Polans A, Baehr W, and Palczewski K. “Turned on by Ca2+! The physiology and pathology of Ca2+-binding proteins in the retina.” Trends in Neurosciences. vol. 19(12). 1996. Pages 547-554
• Ramón y Cajal, Santiago. “Drawing of Layers of Retina.” Online Image. 1911. Wikipedia. 21 Mar. 2008. <http://en.wikipedia.org/wiki/Image:Fig_retine.png>
• Escher, M.C. “Eye.” Online Image. 1946. Pictures by M.C Escher. 15 Mar 2008. <http://aaronbaird.net/pictures/Escher/>
• Omikron, “Magnified image of the rods and cones of the human eye.” Free Health Encyclopedia. 3 Apr. 2008. <http://www.faqs.org/health/Sick-V1/Color-Blindness.html>