Vitamin A

© Image: David E. Volk
Retinol (Vitamin A) and related compounds.

Vitamin A, or retinol, is the immediate precursor of two important biochemicals, retinal and retinoic acid. Ultimately, retinol is derived biochemically from carotenes such as$\beta$-carotene, but is not derived from similar carotenoids such as lutein or zeaxanthin. Retinal plays a critical role in vision, while retinoic acid is an intracellular messenger chemical that affects gene transcription. Although plants do not produce retinol, they do produce carotenes which can be converted to retinol in the gastrointestinal tract.

{{Image|Beta-carotene.png|center|500px|Retinol (Vitamin A) and related compounds.