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From Carrots to April 20, 2005 ©2005 Neocles Leontis.
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Transcript of From Carrots to April 20, 2005 ©2005 Neocles Leontis.
From Carrots to
April 20, 2005©2005 Neocles Leontis
Carrots Contain Carotene -
• The Eleven Double bonds act as an Antenna to absorb visible light (electromagnetic waves!)
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
The Absorption Spectrum of Carotene
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UV and BlueLight Absorbed
Carotene Absorbs Blue Light and so it appears Orange (Complementary
colors)
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UV and BlueLight Absorbed
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
Metabolic Pathways involving retinal
•http://www.genome.jp/dbget-bin/show_pathway?map00830+C02094
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
What does your body do with Retinal?
It goes to the RetinaIn the Eye
The Retina acts as a Screen on which images are
projectedIt goes to the RetinaIn the Eye
The Retina has Light-sensitive Rod and Cone
cellsElectron Micrograph of rodAnd cone cells
http://palaeo-electronica.org/2000_1/retinal/vision.htm
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
This Membrane is folded back and forth many times to increase the
surface area
StackedMembraneDisks -Contain RhodopsinProtein
The Membrane contains the Protein Rhodopsin which binds Retinal
StackedMembraneDisks -Contain RhodopsinProtein
Opsin is a protein -348 amino acids
It passes 7 times through the membrane forming 7 Alpha
Helices
Rhodopsin absorbs Green light - What color is it?
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“Rhodo” = RoseIn Greek
Opsin is a protein made of 348 amino acids connected by amide bonds
Stretched out it is very long!
When it folds up the Opsin protein is much more compact
The folded Opsin forms 7 helical regions (in red) that fold back and forth through the membrane:
Cross your eyes to see 3D!
Retinal
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
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
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
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
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
11-cis Retinal (before absorption of photon of light)
OH
11-cis Retinal
All-trans Retinal (after absorption of photon of light)
OH
11-cis Retinal
O
H
All-trans Retinal
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)
Sequence of Reactions