Question

2. The vitamin C and D are two important nutrients that are essential in the human diet. The structure of each compound is shown below. Some vitamins are excreted in the urine while others are stored in fatty tissue. Based on the structures shown above, predict where each vitamin would most likely be found. Explain your reasoning in each case. (T2] Vitamin C HO-CH HO-C Vitamin D HC CH Hic CH H HO OH CH HO

Answer 1

VITAMIN D

The major natural source of the vitamin is synthesis of cholecalciferol in the lower layers of skin epidermis through a chemical reaction that is dependent on sun exposure (specifically UVB radiation).

The term vitamin D is, unfortunately, an imprecise term referring to one or more members of a group of steroid molecules. Vitamin D₃, also known as cholecalciferol is generated in the skin of animals when light energy is absorbed by a precursor molecule 7-dehydrocholesterol. Vitamin D is thus not a true vitamin, because individuals with adequate exposure to sunlight do not require dietary supplementation.

Vitamin D, as either D₃ or D₂, does not have significant biological activity. Rather, it must be metabolized within the body to the hormonally-active form known as 1,25-dihydroxycholecalciferol. This transformation occurs in two steps, as depicted in the diagram to the right:

1. Within the liver, cholecalciferal is hydroxylated to 25-hydroxycholecalciferol by the enzyme 25-hydroxylase.
2. Within the kidney, 25-hydroxycholecalciferol serves as a substrate for 1-alpha-hydroxylase, yielding 1,25-dihydroxycholecalciferol, the biologically active form.

Each of the forms of vitamin D is hydrophobic, and is transported in blood bound to carrier proteins. The major carrier is called, appropriately, vitamin D-binding protein. The halflife of 25-hydroxycholecalciferol is several weeks, while that of 1,25-dihydroxycholecalciferol is only a few hours.

VITAMIN C

Vitamin C is a water-soluble vitamin, which means it dissolves in water. In contrast to fat-soluble vitamins, water-soluble vitamins do not get stored within the body. ... Since your body does not store vitamin C or produce it on its own, it's important to consume foods that are rich in vitamin C daily