Lecture #14 - Vitamin A

Question 1

What was vitamin A originally discovered for, and what are its active forms?

Answer 1

Vitamin A was originally discovered for its ability to prevent night blindness (xerophthalmia).

Its active forms include retinoids (retinol, retinal, and retinoic acid) found in animal products, and carotenoids (beta-carotene, alpha-carotene, lycopene, and lutein) found in plant foods.

Question 2

How does vitamin A contribute to vision?

Answer 2

Vitamin A contributes to vision by forming rhodopsin in rod cells, a complex structure made of opsin and cis-retinal. This is essential for converting light into visual signals.

Question 3

Describe the process of vitamin A becoming active in the body.

Answer 3

Vitamin A (retinol) can be converted to retinal, and retinal can become retinoic acid, which cannot revert to retinal. Retinoic acid acts in the nucleus of the cell to affect gene expression.

Vitamin A (retinol) –> retinal –> retinoic acid –> affect gene expression

Question 4

How does vitamin A affect gene expression?

Answer 4

Retinoic acid, an active form of vitamin A, enters the nucleus of the cell where it influences gene expression, affecting various bodily functions including vision, immune response, and cellular growth.