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

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
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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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Color Wheel
Complementary
Colors:
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Carotene
absorbs
425 nm!
Carrots are Orange because
the contain Carotene
The Absorption Spectrum of Carotene
UV and Blue
Light Absorbed
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Carotene Absorbs Blue Light and so it
appears Orange (Complementary colors)
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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:
• 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
Beta-Carotene
2 Retinal
•http://www.genome.jp/dbget-bin/show_pathway?map00830+C02094
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 Lightsensitive Rod and Cone cells
Electron Micrograph of rod
And cone cells
http://palaeo-electronica.org/2000_1/retinal/vision.htm
The Retina has Lightsensitive Rod and Cone cells
Electron Micrograph of rod
And cone cells
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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?
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“Rhodo” = Rose
In Greek
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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:
Retinal
Cross your eyes to see 3D!
Here the protein is colored to show the non-polar
amino acids in gray (blue = Pos, red = Neg)
Retinal
Cross your eyes to see 3D!
How does the protein fold up the way
it supposed to EVERY TIME - all by
itself?
Colors of Amino acids:
Gray: Non-polar
Yellow: Uncharged
Red: Negatively charged
Blue: Positively charged
Lipid Membrane
The crystal structure: 1LDH.pdb
http://www.rcsb.org/pdb/cgi/explore.cgi?pid=61711114029056&pdbId=1L9H
The Non-polar Amino Acids are concentrated in
the part of the protein that passes through the
membrane (pink box)
Colors of Amino acids:
Gray: Non-polar
Yellow: Uncharged
Red: Negatively charged
Blue: Positively charged
Green: Retinal
The crystal structure: 1LDH.pdb
http://www.rcsb.org/pdb/cgi/explore.cgi?pid=61711114029056&pdbId=1L9H
The Retinal is attached to the
protein- inside the helices
Colors of Amino acids:
Gray: Non-polar
Yellow: Uncharged
Red: Negatively charged
Blue: Positively charged
Green: Retinal
The crystal structure: 1LDH.pdb
http://www.rcsb.org/pdb/cgi/explore.cgi?pid=61711114029056&pdbId=1L9H
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
11-cis Retinal (before absorption of
photon of light)
H
O
11-cis Retinal
All-trans Retinal (after absorption
of photon of light)
O
H
H
O
11-cis Retinal
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
O
H
H
O
11-cis Retinal
All-trans Retinal
Additional reading: Life Under the Sun, by Peter A. Ensminger, Yale University
Press (ISBN: 0-300-08804-3)
Sequence of Reactions