Vitamin A

Question 1

What are the 3 forms of Vitamin A?

Answer 1

retinol, retinal and retinoic acid

Question 2

Retinol can be converted to retinal and vice versa with help from _________, which ___________ cleaves 1 molecule of retinol into 2 molecules of retinal.

Bonus question: Where does this process happen?

Answer 2

B-carotene, oxidatively

Intestine

Question 3

How is Vitamin A transported and absorbed? What is required for its transfer to extra hepatic tissues? To the nucleus?

Answer 3

• Transported in chylomicrons where it is delivered to the liver and stored in the cells of Ito.
• Requires plasma retinol-binding protein to be carried to extra hepatic tissues. Uses cellular retinol-binding protein to become transported to the nucleus.

Question 4

Location and process of formation of rhodopsin? What happens when rhodopsin is exposed to light?

Answer 4

• In retinal cells, retinol –> retinal –> 11-cis-retinal
• 11-cis-retinal + opsin –> rhodopsin
• With light exposure, rhodopsin –> all-trans-retinal + opsin

Question 5

Retinoic acid is similar in action to _______ hormones. What is its role in the body?

Answer 5

• Steroid/thyroid hormones.

- Gene control of growth genes –> differentiation and maintenance of mucus-secreting cells.

Question 6

Two kinds of retinoic acid receptors? Which one can bine both all-tras-retinoic acid and 9-cis-retinoic acid? Which one is important for vitamin D function?

Answer 6

• RAR and RXR.
• RAR can bind All-trans-retinoic acid plus 9-cis-retinoic acid
• RXR is important for Vitamin D functioning.

Question 7

Symptoms of Vitamin A deficiency?

Answer 7

• Night blindness (nyctalopia: early symptom)
• Xerophthalmia (pathologic dryness of eyes)
• Hyperkeratinization of skin
• Decreased immune system response
  Remember, functions of Vitamin A
• Antioxidant (treatment for measles, retinoic pigmentosum)
• Aura (see light)
• Activation (epithelial cell differentiation)
• Alopecia + Abnormal Pregnancy (problems with excess vitamin A)

Question 8

Hypervitaminosis A, in addition to alopeicia and pregnancy abnormalities, may also result in?

Answer 8

Dry/ pruritic skin, papilledema (edema of optic disc), enlarged and cirrhotic liver, bone problems (joint pain, osteoporosis, hyperstosis) and increased intracranial pressure

Question 9

Where can Vitamin A be found?

Answer 9

Dark green, orange or yellow vegetables. Some diarly products.