What are the Most Important Functions of Vitamin A?

Vitamin A (Fat Soluble Vitamins)

Free Online Lectures of Biochemistry for Medical, Dental and Allied Health Sciences by Biochemistry Club

  • Vitamin A is a Fat soluble vitamin.
  • Its active form is only present in animals.
  • In plants it is present in the  form of a pro-vitamin called Beta-carotene.
  • All the compounds with Vitamin A activity are referred to as Retinoids (Poly-isoprenoid compounds having a beta-ionone (cyclohexenyl) ring system).
  • Three different compounds with Vitamin A activity are:
  1. Retinol – Vitamin A alcohol
  2. Retinal – Vitamin A aldehyde and
  3. Retinoic acid – Vitamin A acid.


The term Retinoids,  collectively refers to various forms of Natural & Synthetic Vitamin A.

  1. Retinol is a primary alcohol with a β-ionone ring and Unsaturated fatty acids.
  2. Retinal also called as Retinaldehyde is the aldehyde form of retinol.
  3. Retinoic acid is the oxidized form of retinal.
  4. 11-cis retinal is the isomer of all-trans retinal.
  5. β-carotene is found in plants. It yields 2 molecules of retinal upon oxidation.

Structure of Vitamin A

  • In the structure of Vitamin A, the side chain contains alternate double bonds.
  • Due to the presence of a number of double bonds many isomers are possible.
  • The all-trans variety of retinal, also called Vitamin A1 is the most common type.
  • Vitamin A2 is found in fish oils and has an extra double bond in the ring.
  • Biologically important compound of Vitamin A  is the 11-cis-retinal.

All these lectures are organized and listed in detail in their proper sections. To view these lessons please visit the Vitamins Section. This can be approached by directly clicking the Biochemistry I button or it can also be approached from the drop down menu in Biochemistry I tab. Once you reach the section click the curriculum tab to view the full list in the section.

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