Vitamin A

Question 1

What is vitamin A?

Answer 1

A fat soluble vitamin present only in foods of animal origin

Vitamin A has provitamins called carotenes found in plants.

Question 2

What are the vitamers of vitamin A?

Answer 2

Retinol, retinal, and retinoic acid

These are structurally related and biologically active molecules.

Question 3

What is retinol?

Answer 3

Vitamin A alcohol, a primary alcohol containing B-ionone ring and two isoprenoid units

Retinol is one of the key forms of vitamin A.

Question 4

What is retinal?

Answer 4

Vitamin A aldehyde, obtained by the oxidation of retinol

Retinal plays a crucial role in vision.

Question 5

Fill in the blank: Retinol is a primary alcohol containing a _______ ring.

Answer 5

B-ionone

Question 6

True or False: Vitamin A is only found in plant sources.

Answer 6

False

Question 7

What are the two main types of vitamin A found in animal foods?

Answer 7

Retinol and retinal

These forms are crucial for various biological functions.

Question 8

Fill in the blank: The term vitamin A is collectively used to represent many _______ molecules.

Answer 8

structurally related and biologically active

Question 9

What is retinoic acid?

Answer 9

Produced by the oxidation of retinal

Retinoic acid is also known as vitamin A acid.

Question 10

What is B-Carotene?

Answer 10

A provitamin A found in plant foods

B-Carotene is cleaved in the intestine to produce retinal.

Question 11

What is the conversion efficiency of B-Carotene to vitamin A in humans?

Answer 11

About one-sixth vitamin A activity compared to retinol

This indicates that humans convert B-carotene to retinal inefficiently.

Question 12

How are dietary retinyl esters processed in the intestine?

Answer 12

Hydrolysed by pancreatic or intestinal brush border hydrolases

This process releases retinol and free fatty acids.

Question 13

What enzyme hydrolyses carotenes in intestinal cells?

Answer 13

B-carotene 15-15’-dioxygenase

This enzyme releases 2 moles of retinal from carotenes.

Question 14

What happens to retinol in intestinal mucosal cells?

Answer 14

Reesterified to long chain fatty acids and incorporated into chylomicrons

Retinol esters are then transferred to the lymph.

Question 15

How is retinol transported in the circulation?

Answer 15

By the plasma retinol binding protein

This protein ensures retinol is delivered to various tissues.

Question 16

What role do cellular retinol-binding proteins play?

Answer 16

Carry retinol to the nucleus and bind to chromatin (DNA)

This binding allows retinol to exert its function similarly to a steroid hormone.

Question 17

Fill in the blank: Retinol is stored in the _______.

Answer 17

liver

The liver acts as a reservoir for retinol esters from chylomicrons.

Question 18

What is the primary event in the visual cycle?

Answer 18

The isomerization of 11-cis-retinal to all-trans-retinal

This event occurs upon exposure to light and is crucial for the generation of nerve impulses

Question 19

What is rhodopsin composed of?

Answer 19

11-cis retinal and the protein opsin

Rhodopsin is a conjugated protein present in rods and is essential for light vision

Question 20

What is the recommended dietary allowance (RDA) of vitamin A for adults?

Answer 20

0.3 mg of retinol

The requirement increases in pregnant women and lactating mothers

Question 21

What is the function of vitamin A in the process of vision?

Answer 21

It is involved in the conversion of 11-cis retinal to participate in the visual cycle

Vitamin A also plays roles in reproduction and maintenance of epithelial cells

Question 22

True or False: The human eye has about 10 million rods and cones.

Answer 22

False

The human eye has about 120 million rods and 6 million cones

Question 23

What is the daily requirement of beta-carotene for maintaining healthy vision?

Answer 23

600 pg/day (or 4800 µg of beta-carotene)

Beta-carotene is beneficial in preventing oxidative damage and supports vision

Question 24

Fill in the blank: The all-trans-retinal is immediately converted to _______ after isomerization.

Answer 24

all-trans retinol

This conversion is part of the visual cycle initiated by light exposure

Question 25

Who elucidated the visual cycle first?

Answer 25

George Wald ## Footnote He received a Nobel Prize for his work in 1968

Question 26

What types of cells are present in the retina of the eye?

Answer 26

Rods and cones ## Footnote Rods are responsible for dim light vision while cones are involved in bright light and color vision

Question 27

What are carotenoids known for in relation to health?

Answer 27

They act as antioxidants and reduce the risk of age-related attacks ## Footnote Carotenoids are important for maintaining healthy vision and overall health

Question 28

What biochemical functions does vitamin A serve?

Answer 28

Vision, proper growth and differentiation, reproduction, maintenance of epithelial cells ## Footnote Vitamin A is essential for a variety of bodily functions

Question 29

What is the best dietary source of preformed vitamin A?

Answer 29

Liver, kidney, egg yolk, milk, cheese, and butter ## Footnote Fish liver oils, particularly from cod or shark, are also very rich in vitamin A.

Question 30

Which vegetables are good sources of provitamin A-carotenes?

Answer 30

Yellow and dark green vegetables and fruits such as carrots, spinach, amaranthus, pumpkins, mango, and papaya ## Footnote These vegetables and fruits contain carotenoids that can be converted into vitamin A.

Question 31

What condition can result from prolonged xerophthalmia due to vitamin A deficiency?

Answer 31

Keratomalacia, leading to total blindness ## Footnote Keratomalacia involves the destruction of the cornea.

Question 32

What is the most common cause of blindness in children in developing countries?

Answer 32

Vitamin A deficiency blindness

Question 33

What is one of the earliest symptoms of vitamin A deficiency?

Answer 33

Night blindness (nyctalopia) ## Footnote Individuals experience difficulty seeing in dim light due to impaired adaptation.

Question 34

What severe condition is characterized by dryness in conjunctiva and cornea?

Answer 34

Xerophthalmia ## Footnote This condition can lead to keratinization of epithelial cells.

Question 35

What are Bitot's spots?

Answer 35

White triangular plaques seen in certain areas of conjunctiva ## Footnote Bitot's spots are associated with vitamin A deficiency.

Question 36

What is the best dietary source of preformed vitamin A?

Answer 36

Liver, kidney, egg yolk, milk, cheese, and butter ## Footnote Fish liver oils, particularly from cod or shark, are also very rich in vitamin A.

Question 37

Which vegetables are good sources of provitamin A-carotenes?

Answer 37

Yellow and dark green vegetables and fruits such as carrots, spinach, amaranthus, pumpkins, mango, and papaya ## Footnote These vegetables and fruits contain carotenoids that can be converted into vitamin A.

Question 38

What condition can result from prolonged xerophthalmia due to vitamin A deficiency?

Answer 38

Keratomalacia, leading to total blindness ## Footnote Keratomalacia involves the destruction of the cornea.

Question 39

What is the most common cause of blindness in children in developing countries?

Answer 39

Vitamin A deficiency blindness

Question 40

What is one of the earliest symptoms of vitamin A deficiency?

Answer 40

Night blindness (nyctalopia) ## Footnote Individuals experience difficulty seeing in dim light due to impaired adaptation.

Question 41

What severe condition is characterized by dryness in conjunctiva and cornea?

Answer 41

Xerophthalmia ## Footnote This condition can lead to keratinization of epithelial cells.

Question 42

What are Bitot's spots?

Answer 42

White triangular plaques seen in certain areas of conjunctiva ## Footnote Bitot's spots are associated with vitamin A deficiency.