1. From Carrots to April 20, 2005 ©2005 Neocles Leontis

2. Carrots Contain Carotene - The Eleven Double bonds act as an Antenna to absorb visible light (electromagnetic waves!)

3. Colors and Wavelength Violet: 400 - 420 nm Indigo: 420 - 440 nm Blue: 440 - 490 nm Green: 490 - 570 nm Yellow: 570 - 585 nm Orange: 585 - 620 nm Red: 620 - 780 nm

4. Carotene absorbs 425 nm! Color Wheel Complementary Colors:

5. Carrots are Orange because the contain Carotene

6. The Absorption Spectrum of Carotene UV and Blue Light Absorbed

7. Carotene Absorbs Blue Light and so it appears Orange (Complementary colors) UV and Blue Light Absorbed

8. What happens to Carotene after you eat a Carrot? Find out at the KEGG Web site (Kyoto Encyclopedia of Genes and Genomics) Carotene is converted to Retinol (Vitamin A) as shown on the KEGG website: http://www.genome.jp/dbget-bin/show_pathway?map00830+C02094

9. Metabolic Pathways involving retinal http://www.genome.jp/dbget-bin/show_pathway?map00830+C02094

10. Reaction converting Carotene to 2 molecules of Retinal http://www.genome.jp/dbget-bin/show_pathway?map00830+C02094 Beta-Carotene 2 Retinal

11. What does your body do with Retinal? It goes to the Retina In the Eye

12. The Retina acts as a Screen on which images are projected It goes to the Retina In the Eye

13. The Retina has Light- sensitive Rod and Cone cells Electron Micrograph of rod And cone cells http://palaeo-electronica.org/2000_1/retinal/vision.htm

14. The Retina has Light- sensitive Rod and Cone cells Electron Micrograph of rod And cone cells

15. Rod and Cone Cells contain Internal Lipid membranes containing Rhodopsin Stacked Membrane Disks - Absorb Light

16. This Membrane is folded back and forth many times to increase the surface area Stacked Membrane Disks - Contain Rhodopsin Protein

17. The Membrane contains the Protein Rhodopsin which binds Retinal Stacked Membrane Disks - Contain Rhodopsin Protein

18. Opsin is a protein -348 amino acids It passes 7 times through the membrane forming 7 Alpha Helices

19. Rhodopsin absorbs Green light - What color is it? “Rhodo” = Rose In Greek

20. Opsin is a protein made of 348 amino acids connected by amide bonds Stretched out it is very long!

21. When it folds up the Opsin protein is much more compact

22. The folded Opsin forms 7 helical regions (in red) that fold back and forth through the membrane: Cross your eyes to see 3D! Retinal

23. Here the protein is colored to show the non-polar amino acids in gray (blue = Pos, red = Neg) Cross your eyes to see 3D! Retinal

24. How does the protein fold up the way it supposed to EVERY TIME - all by itself? The crystal structure: 1LDH.pdb http://www.rcsb.org/pdb/cgi/explore.cgi?pid=61711114029056&pdbId=1L9H Colors of Amino acids: Gray: Non-polar Yellow: Uncharged Red: Negatively charged Blue: Positively charged Lipid Membrane

25. The Non-polar Amino Acids are concentrated in the part of the protein that passes through the membrane (pink box) The crystal structure: 1LDH.pdb http://www.rcsb.org/pdb/cgi/explore.cgi?pid=61711114029056&pdbId=1L9H Colors of Amino acids: Gray: Non-polar Yellow: Uncharged Red: Negatively charged Blue: Positively charged Green: Retinal

26. The Retinal is attached to the protein- inside the helices The crystal structure: 1LDH.pdb http://www.rcsb.org/pdb/cgi/explore.cgi?pid=61711114029056&pdbId=1L9H Colors of Amino acids: Gray: Non-polar Yellow: Uncharged Red: Negatively charged Blue: Positively charged Green: Retinal

27. Top view showing the Retinal inside the helices (in the plane of the membrane) The crystal structure: 1LDH.pdb http://www.rcsb.org/pdb/cgi/explore.cgi?pid=61711114029056&pdbId=1L9H

28. 11-cis Retinal (before absorption of photon of light) 11-cis Retinal

29. All-trans Retinal (after absorption of photon of light) 11-cis RetinalAll-trans Retinal

30. The change in shape of the Retinal affects the Opsin protein - leading to Signal Transduction, and eventually an electrical signal to the brain via the optic nerve 11-cis RetinalAll-trans Retinal Additional reading: Life Under the Sun, by Peter A. Ensminger, Yale University Press (ISBN: 0-300-08804-3)

31. Sequence of Reactions