Question
Identify the Enzymes :1 and 2 as shown in the image.
A. Enzyme 1 : 1 alpha hydoxylase
Enzyme 2 : 25 hydroxylase
B. Enzyme 1 : 1 alpha dehydroxylase
Enzyme 2 : 25 dehydroxylase
C. Enzyme 1 : 25 hydroxylase
Enzyme 2 : 1 alpha hydoxylase
D. Enzyme 1 : 1 beta hydroxylase
Enzyme 2 : 25 hydroxylase
Show Answer
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Correct Answer ยป C
Explanation
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Ans:C.
Enzyme 1 : 25 hydroxylase
Enzyme 2 : 1 alpha hydroxylase.
Synthesis of Vitamin D is shown in the image.
Vitamin D
- Vitamin D is the major vitamin involved in the absorption of calcium.
- Beside dietary intake, cutaneous synthesis is the other and more important source of vitamin D (cholecalciferol) in the body. The keratinocytes of stratum corneum of the epidermis of skin contain 7-dehydrocholesterol which is converted to Vitamin D3(cholecalciferol) by the action of sunlight (UV light).
- This vitamin D3 (Cholecalciferol) is converted to calcidiol (calcifediol or 25 hydroxy cholecalciferol or 25-hydroxy vitamin D3) by 25 hydroxylase in the liver.
- Calcidiol is the major circulating form of vitamin D3.
- Calcidiol is then converted to Calcitriol (1-25 dihydroxy-cholecalciferol or 1-25 dihydroxy vitamin D3) by 1-a hydroxylation in kidney.
- The final hydroxylation in kidney is rate limiting step.
- Calcitriol is the active form of vitamin D.
- Dietary vitamin D is absorbed in ileum and requires bile salts.
When Ca2 level is high, little calcitriol is produced, and the kidney produce the relatively inactive metabolite 24, 25 dihydroxycholecalciferol instead.
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