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