Chemistry



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Bog'liq
vitamin a mn

  • VITAMIN A
  • Dr Manisha

CHEMISTRY

  • Common structural unit
  • A trimethyl cyclohexenyl ring
  • An all trans configured chain with four double bonds.
  • Retinoic acid

TYPES

  • Retinol - when R is -CH2OH
  • Retinal - when R is -CHO
  • Retinoic acid –when R is -COOH

FORMS OF VITAMIN A

  • VITAMIN A1 – found in major species of animals.
  • VITAMIN A2- found in fresh water fish.
  • NEOVITAMIN A- stereoisomer of vitamin A1

COMPARISON

  • VIT A1
  • Found in major species of animals
  • Only one double bond in beta ionone ring.
  • More potent
  • Can be obtained through carotenes
  • VIT A2
  • Found in freshwater fish
  • Two double bonds in beta ionone ring
  • Activity 40% of A1
  • Carotenes can not give rise to vitamin A2

DIETARY SOURCES

  • Animal sources- liver oil,butter,milk, cheese,egg- yolk,
  • Plant sources- tomatoes,carrots,green yellow vegetables,spinach and fruits like mangoes,papayas,corn,sweet potatoes

Recommended Daily Allowance

  • Adult male- 3000 IU
  • Adult female- 3000 IU
  • Recommended daily allowance is 6000IU
  • 1 IU=0.3 micro gms of Retinol

ABSORPTION, STORAGE & TRANSPORT

  • ABSORBED IN SMALL INTESTINE
  • FREE retinol is absorbed
  • Retinol is transported in association with a specific retinol binding protein .
  • Stored as retinyl ester (normally as retinyl palmitate)
  • Retinoic acid is transported in association with a specific retinoic acid binding protein .

ROLE IN VISION

  • Overall mechanism through which it works is known as Wald’s visual cycle /rhodopsin cycle.
  • Rods contain –photosensitive pigment called rhodopsin or visual purple.
  • Visual purple –opsin
  • retinine/retinal or retinaldehyde

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