Short Answer Questions - Vitamins
1. What are the fat-soluble vitamins?
Vitamins A, D, E and K.
2. Why is a deficiency of the fat-soluble vitamins seen in cystic fibrosis?
In cystic fibrosis, decreased secretion of pancreatic lipase results in impaired absorption of fat from the intestines (steatorrhoea). Consequently, fat-soluble vitamins will be egested in the stools.
3. What are the functions of vitamin A?
Vitamin A is used in the visual cycle and it also has a role in regulating gene expression.
4. Why is vitamin D known as 'the sunshine vitamin'?
Sunlight radiation is needed to convert precursors of vitamin D into cholecalciferol which can be further metabolised to active 1,25-dihydroxycholecalciferol (1,25-DHCC).
5. What are the functions of vitamin D?
The active form of vitamin D (1,25-dihydroxycholecalciferol (1,25-DHCC)) controls calcium metabolism. It increases blood calcium by stimulating resorption of calcium from bone, increasing renal reabsorption of calcium and intestinal absorption of calcium.
6. What are the functions of vitamin E?
Vitamin E is an antioxidant. It prevents free radical damage to membranes, especially to the polyunsaturated fatty acids in erythrocyte membranes.
7. What are the clinical consequences of vitamin E deficiency?
Fragile erythrocytes and damage to nerve cells.
8. What is the function of vitamin K?
Vitamin K promotes γ-carboxylation of glutamate residues on proteins involved in blood clotting.
9. What are the clinical consequences of vitamin K deficiency?
Haemorrhagic disease of the newborn.
10. What is the function of vitamin B1 (thiamin)?
Thiamin pyrophosphate is a coenzyme for pyruvate dehydrogenase, a-ketoglutarate dehydrogenase, the branched-chain a-ketoacid dehydrogenases and transketolase (pentose phosphate pathway).
11. What are the clinical consequences of vitamin B1 deficiency?
Glucose metabolism is impaired, resulting in decreased production of ATP. Beriberi; Wernicke–Korsakoff syndrome.
12. What is the function of vitamin B2 (riboflavin)?
Riboflavin is a component of FAD and FMN. FAD is important in oxidation/reduction reactions, e.g. in acyl CoA dehydrogenase (ß-oxidation). FMN is a component of the respiratory chain.
13. What are the clinical consequences of vitamin B2 deficiency?
Inflamed, magenta-coloured tongue and angular cheilosis.
14. What is the function of vitamin B3 (niacin)?
Niacin is a component of NAD+ and NADP+ and therefore is important in numerous oxidation/reduction reactions, e.g. in glycolysis, Krebs cycle and ß-oxidation.
15. What is the clinical consequence of vitamin B3 deficiency?
Pellagra.
16. What is the function of vitamin B5 (pantothenate)?
Pantothenate is a component of coenzyme A which is a coenzyme for numerous enzymes involved in carbohydrate, protein and lipid metabolism, e.g. pyruvate dehydrogenase, long chain acyl CoA synthetase.
17. What are the clinical consequences of vitamin B5 deficiency?
Pantothenic acid deficiency is very rare; ‘burning feet syndrome’ seen in prisoners of war.
18. What is the function of vitamin B6 (pyridoxine)?
Pyridoxal phosphate is needed for transamination reactions (e.g. alanine aminotransferase (ALT) and aspartate aminotransferase (AST)). It is also needed for a wide range of reactions, e.g. glycogen phosphorylase and kynureninase (essential for niacin biosynthesis).
19. What are the clinical consequences of vitamin B6 deficiency?
Inflammation of tongue, lips and mouth.
20. What is the function of vitamin B12?
Vitamin B12 has two active forms: (i) methylcobalamin, which is needed for methionine synthase (also known as homocysteine methyltransferase) essential for the methionine salvage pathway, and (ii) deoxyadenosylcobalamin, which is needed for methylmalonyl CoA mutase.
21. What are the clinical consequences of vitamin B12 deficiency?
Megaloblastic anaemia and neuropathy.
22. What is the function of folic acid?
Folate is converted to tetrahydrofolate which is a carrier for ‘1-carbon’ units (formyl, methenyl, methylene and methyl). These are especially important for biosynthesis of the purine and pyrimidine bases which are components of DNA and RNA. Therefore, folate is essential for cell growth and cell division.
23. What is the clinical consequence of folic acid deficiency?
Megaloblastic anaemia.
