Download MBBS (Bachelor of Medicine, Bachelor of Surgery) 1st year (First Year) Biochemistry ppt lectures Topic 88 Vitamin A Notes. - biochemistry notes pdf, biochemistry mbbs 1st year notes pdf, biochemistry mbbs notes pdf, biochemistry lecture notes, paramedical biochemistry notes, medical biochemistry pdf, biochemistry lecture notes 2022 ppt, biochemistry pdf.
VITAMIN A
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
VIT A2
1.
Found in major species of
animals
1.
Found in freshwater
fish
2.
Only one double bond in beta
ionone ring.
2.
Two double bonds in
beta ionone ring
3.
More potent
3.
Activity 40% of A1
4.
Can be obtained through
carotenes
4.
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
v Adult male- 3000 IU
v Adult female- 3000 IU
v Recommended daily allowance is 6000IU
v 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
Bathorhodopsin
RHODOPSIN
Light
Lumirhodopsin
Metarhodopsin-I
Dark
Metarhodopsin-II
Isomerase
opsin
opsin
Cis-retinal
Trans-retinal
Blue light
Retinene reductase
Retinene reductase
Isomerase
Trans-retinol
Cis-retinol
Blue light
WALD'S VISUAL CYCLE
EPITHELIAIZATON
Epithelial structures show gross
structural changes in deficiency
Skin-dry,rough& scaly
Cornea-epithilium keratinised,opaque
Bitot's spot
Lacrimal glands-similar changes
leading to dryness of
conjunctiva&cornea(xerophthalmia)
Respiratory tract ?keratinzation-
susceptibility to infection.
BONE AND TEETH FORMATION
Deficiency results in slowing of endochondral bone
formation and reduced osteoblastic activity.
Thinning of enamel and deposit of chalky deposit on the
surface of the teeth.
ROLE IN REPRODUCTION
EXPERIMENTS ON RATS-
Deficient male-ill developed testes, immature sperms
Deficient female-unable to carry pregnancy to full term
.
ROLE IN METABOLISM-
Protein synthesis
DNA metabolism
Beta-Carotene as an
antioxidant and anticancer
In addition to its antioxidant property, Beta- Carotene
also has been shown to have anticancer action.
It increases the number of receptors on WBC for a
molecule known as "major histocompatibility complex
I".
OCULAR MENIFASTATIONS- VITAMIN A
DEFICIENCY
Night blindness/ Nyctalopia-first symptom
Conjunctival xerosis-first clinical sign
Bitot's spot-frequently bilateral
Corneal xerosis-cornea dry & nonwettable
Keratomalacia-ulceration of cornea.
Extra ocular manifestations
vitamin A deficiency
Follicular hyperkeratosis
Anorexia
Growth retardation
Increased respiratory & intestinal infection
HYPER VITAMINOSIS A
Alteration of skin
Hepatic dysfunction
Headache
Drowsiness
CHRONIC EFFECTS-
Roughening of skin,desquamation
Irritability
Coarsening of skin&falling of hair
Anorexia
Wt loss
THERAPEUTIC USES OF
RETINOIC ACID
Oral leukoplakia
Promyelocytic leukaemia
MCQ
Worldwide, the most common vitamin
deficiency is that of
(A) Ascorbic acid (B) Folic acid
(C) Vitamin A (D) Vitamin D
Vitamin A or retinal is a
(A) Steroid
(B) Polyisoprenoid compound containing a
cyclohexenyl ring
(C) Benzoquinone derivative
(D) 6-Hydroxychromane
-Carotene, precursor of vitamin A, is
oxidatively cleaved by
(A) -Carotene dioxygenase
(B) Oxygenase
(C) Hydroxylase
(D) Transferase
The international unit of vitamin A is
equivalent to the activity caused by
(A) 0.3 g of Vitamin A alcohol
(B) 0.344 g of Vitamin A alcohol
(C) 0.6 g of Vitamin A alcohol
(D) 1.0 g of Vitamin A alcohol
Retinol is transported in blood bound to
(A) Aporetinol binding protein
(B) 2-Globulin
(C) -Globulin
(D) Albumin
Deficiency of Vitamin A causes
(A) Xeropthalmia
(B) Hypoprothrombinemia
(C) Megaloblastic anemia
(D) Pernicious anemia
Retinal is a component of
(A) Iodopsin (B) Rhodopsin
(C) Cardiolipin (D) Glycoproteins
An important function of vitamin A is
(A) To act as coenzyme for a few enzymes
(B) To play an integral role in protein synthesis
(C) To prevent hemorrhages
(D) To maintain the integrity of epithelial tissue
Conversion of all-trans-retinal into alltrans-
retinol requires
(A) NAD (B) NADH
(C) NADP (D) NADPH
Two molecules of vitamin A can be formed
from 1 molecule of
(A) -Carotene (B) -Carotene
(C) -Carotene (D) All of these
This post was last modified on 05 April 2022