Bio Unit 2.1 Discussion - (5 Please discuss the structure...

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(5). Please discuss the structure and function of vitamin D, and give an example to describe the consequences of vitamin D deficiency. Vitamin D3, which is also known as “cholecalciferol” results when 7-hydrocholesterol (or cholesterol that actually has an extra double bond at carbon 7) is irradiated by UV light (wavelength 290-315 nm) in the skin. What happens after irradiation is that the B ring of the steroid nucleus opens to form secosterol, also known as previtamin D3 (Holick et al., 1980). Warmth will cause further rearrangement of the molecule that eventually results in vitamin D3 (cholecalciferol) itself. In humans and animals, cholecalciferol naturally occurs (e.g., cod liver oil, fatty fish, butter and animal liver). Similarly, Vitamin D2 results when ergosterol, which is a phytosterol…or plant or fungal sterol, is irradiated by UV light. After UV irradiation occurs, chemical changes result in “ergocalciferol.” Ergocalciferol is actually commonly used as a pharmaceutical chemical (known as “calciferol” for short), and is used to fortify some foods with vitamin D (e.g., milk and margarine). Ergosterol and ergocalciferol (Vitamin D2) differs from 7- hydrocholesterol and cholecalciferol (Vitamin D3) from having an additional double bond at carbon-22 as well as an additional methyl group at carbon-24 in the side chain.
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