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From Carrots to
April 20, 2005©2005 Neocles Leontis
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Carrots Contain Carotene -
• The Eleven Double bonds act as an Antenna to absorb visible light (electromagnetic waves!)
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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
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Carotene absorbs425 nm!
Color WheelComplementaryColors:
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Carrots are Orange because the contain Carotene
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The Absorption Spectrum of Carotene
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UV and BlueLight Absorbed
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Carotene Absorbs Blue Light and so it appears Orange (Complementary
colors)
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UV and BlueLight Absorbed
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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
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Metabolic Pathways involving retinal
•http://www.genome.jp/dbget-bin/show_pathway?map00830+C02094
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Reaction converting Carotene to 2 molecules of Retinal
•http://www.genome.jp/dbget-bin/show_pathway?map00830+C02094
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Beta-CaroteneQuickTime™ and a
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2 Retinal
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What does your body do with Retinal?
It goes to the RetinaIn the Eye
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The Retina acts as a Screen on which images are
projectedIt goes to the RetinaIn the Eye
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The Retina has Light-sensitive Rod and Cone
cellsElectron Micrograph of rodAnd cone cells
http://palaeo-electronica.org/2000_1/retinal/vision.htm
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The Retina has Light-sensitive Rod and Cone
cellsElectron Micrograph of rodAnd cone cells
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Rod and Cone Cells contain Internal Lipid membranes containing
Rhodopsin
StackedMembraneDisks -AbsorbLight
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This Membrane is folded back and forth many times to increase the
surface area
StackedMembraneDisks -Contain RhodopsinProtein
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The Membrane contains the Protein Rhodopsin which binds Retinal
StackedMembraneDisks -Contain RhodopsinProtein
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Opsin is a protein -348 amino acids
It passes 7 times through the membrane forming 7 Alpha
Helices
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Rhodopsin absorbs Green light - What color is it?
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“Rhodo” = RoseIn Greek
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Opsin is a protein made of 348 amino acids connected by amide bonds
Stretched out it is very long!
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When it folds up the Opsin protein is much more compact
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The folded Opsin forms 7 helical regions (in red) that fold back and forth through the membrane:
Cross your eyes to see 3D!
Retinal
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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
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How does the protein fold up the way it supposed to EVERY TIME -
all by itself?
The crystal structure: 1LDH.pdbhttp://www.rcsb.org/pdb/cgi/explore.cgi?pid=61711114029056&pdbId=1L9H
Colors of Amino acids: Gray: Non-polarYellow: UnchargedRed: Negatively chargedBlue: Positively charged
Lipid Membrane
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The Non-polar Amino Acids are concentrated in the part of the protein that passes
through the membrane (pink box)
The crystal structure: 1LDH.pdbhttp://www.rcsb.org/pdb/cgi/explore.cgi?pid=61711114029056&pdbId=1L9H
Colors of Amino acids: Gray: Non-polarYellow: UnchargedRed: Negatively chargedBlue: Positively chargedGreen: Retinal
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The Retinal is attached to the protein- inside the helices
The crystal structure: 1LDH.pdbhttp://www.rcsb.org/pdb/cgi/explore.cgi?pid=61711114029056&pdbId=1L9H
Colors of Amino acids: Gray: Non-polarYellow: UnchargedRed: Negatively chargedBlue: Positively chargedGreen: Retinal
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Top view showing the Retinal inside the helices (in the plane of
the membrane)
The crystal structure: 1LDH.pdbhttp://www.rcsb.org/pdb/cgi/explore.cgi?pid=61711114029056&pdbId=1L9H
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11-cis Retinal (before absorption of photon of light)
OH
11-cis Retinal
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All-trans Retinal (after absorption of photon of light)
OH
11-cis Retinal
O
H
All-trans Retinal
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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
OH
11-cis Retinal
O
H
All-trans Retinal
Additional reading: Life Under the Sun, by Peter A. Ensminger, Yale University Press (ISBN: 0-300-08804-3)
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Sequence of Reactions