Download MBBS Biochemistry PPT 88 Vitamin A Lecture Notes

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