Quiz
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1. Why do vitamins A, D, E and K dissolve in fat rather than water?
They are made mostly of carbon and hydrogen (built from isoprene units), with few OH groups (Figure 2).
2. What is isoprene?
A five-carbon building block, C5H8, that plants and animals join to make molecules like retinol and carotenoids (Figure 2).
3. What is the difference between retinol and retinal?
Retinol ends in CH2OH; retinal ends in CH=O (two hydrogens fewer) (Figure 3).
4. Why is beta-carotene called provitamin A?
The body can cut it in the middle and turn each half into retinal (Figure 3).
5. Why is preformed vitamin A a concern in pregnancy?
Large amounts, mainly from supplements or lots of liver, can cause birth defects (Figure 3).
6. What does UVB light do to 7-dehydrocholesterol in the skin?
It breaks open the second ring, forming vitamin D3 (Figure 4).
7. Where is vitamin D activated?
An OH is added in the liver, then a second in the kidney, making calcitriol (Figure 4).
8. Name two deficiency diseases of vitamin D.
Rickets in children, osteomalacia in adults (Figure 4).
9. What part of vitamin E does the antioxidant work?
The OH on its ring head, which gives up a hydrogen to stop a chain reaction (Figure 5).
10. How do alpha- and gamma-tocopherol differ?
Gamma lacks one methyl group on the ring; only alpha counts toward vitamin E needs (Figure 5).
11. Why do newborns get a vitamin K injection?
Little vitamin K crosses the placenta and breast milk is low in it, so babies risk bleeding (Figure 6).
12. Which vitamin must be listed on every US Nutrition Facts label?
Vitamin D (Figure 7).