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: nm Indigo: nm Blue: nm Green: nm Yellow: nm Orange: nm Red: nm

Carotene absorbs 425 nm! Color Wheel Complementary Colors:

Carrots are Orange because the contain Carotene

The Absorption Spectrum of Carotene UV and Blue Light Absorbed

Carotene Absorbs Blue Light and so it appears Orange (Complementary colors) UV and Blue Light 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:

Metabolic Pathways involving retinal

Reaction converting Carotene to 2 molecules of Retinal Beta-Carotene 2 Retinal

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

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

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

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

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

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

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

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? “Rhodo” = Rose In 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.pdb Colors of Amino acids: Gray: Non-polar Yellow: Uncharged Red: Negatively charged Blue: 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.pdb Colors of Amino acids: Gray: Non-polar Yellow: Uncharged Red: Negatively charged Blue: Positively charged Green: Retinal

The Retinal is attached to the protein- inside the helices The crystal structure: 1LDH.pdb Colors of Amino acids: Gray: Non-polar Yellow: Uncharged Red: Negatively charged Blue: Positively charged Green: Retinal

Top view showing the Retinal inside the helices (in the plane of the membrane) The crystal structure: 1LDH.pdb

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

All-trans Retinal (after absorption of photon of light) 11-cis RetinalAll-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 11-cis RetinalAll-trans Retinal Additional reading: Life Under the Sun, by Peter A. Ensminger, Yale University Press (ISBN: )

Sequence of Reactions