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Vitamin A, or retinol, is a 20-carbon lipid molecule obtained in the diet either directly or indirectly from β-carotene [Monday's Molecule #40]. Carrots and other yellow vegetables are rich in β-carotene, a 40-carbon plant lipid whose enzymatic oxidative cleavage yields vitamin A.
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Vitamin A exists in three forms that differ in the oxidation state of the terminal functional group: the stable alcohol retinol, the aldehyde retinal, and retinoic acid. All three compounds have important biological functions. Retinoic acid is a signal compound that binds to receptor proteins inside cells; the ligand–receptor complexes then bind to chromosomes and can regulate gene expression during cell differentiation. The aldehyde retinal is a light sensitive compound with an important role in vision. Retinal is the prosthetic group of the protein rhodopsin; absorption of a photon of light by retinal triggers a neural impulse.
From Horton et al. Principles of Biochemistry, 4th ed. © 2007, Laurence A. Moran and Pearson/Prentice Hall
[Photo Credit: The picture of the carrots is from The Food Network.]
1 comment :
Excellent post, a wonderful example of how to popularize science. Concise, clear, exact. I posted a link to it from my blog. By the way, yours is perhaps the best science blog in blogosphere, congrats.
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