BIOCHEMISTRY in Questions and Answers - Alimov A.M. - 2016

SECTION 2. VITAMINS

Question 1. What are Vitamins?

Answer: Vitamins are low-molecular-weight Organic compounds involved in METABOLISM and characterized by high biological activity. They are not synthesized in the human or animal body and must be obtained from food. They are required in small amounts and are essential for maintaining life, growth, and reproduction.

Question 2. What is the Biological Role of vitamins?

Answer: Vitamins perform one of their primary Functions by participating, alongside other factors, in various enzymatic reactions as Coenzymes.

Question 3. How are vitamins designated and named?

Answer: Vitamins are conventionally designated by capital letters of the Latin alphabet (A, D, E, B1, B₂, etc.), as well as by the disease they prevent, using the prefix "anti-" (e.g., antixerophthalmic, antineuritic, etc.), or by their chemical (or trivial) names, such as retinol, calciferol, biotin, ascorbic acid, etc.

Question 4. How are vitamins classified according to their physicochemical properties?

Answer: Water-soluble and fat-soluble.

Question 5. Which vitamins are classified as fat-soluble?

Answer: Vitamins A, D, E, K, and F (essential polyunsaturated Fatty acids).

Question 6. What are the types of Water-Soluble Vitamins?

Answer: B-group vitamins, C, P, and H.

Question 7. Which vitamins belong to the B group?

Answer: Thiamine (B₁), riboflavin (B₂), pyridoxine (B₆), niacin (PP), biotin (H), pantothenic acid, folic acid (B_c), and cobalamin (B₁₂).

Question 8. What are provitamins?

Answer: Provitamins are substances that lack vitamin activity themselves but can be converted into vitamins within the body.

Question 9. What are hypovitaminosis and avitaminosis?

Answer: Hypovitaminosis is a condition associated with an insufficient intake of a vitamin into the body. Avitaminosis is a pathological state caused by the complete absence of vitamin intake.

Question 10. What is hypervitaminosis?

Answer: Hypervitaminosis is a condition associated with an excessive intake of a vitamin into the body.

Question 11. An excess of which vitamins can cause hypervitaminosis?

Answer: A, D, F, K.

Question 12. Which foods contain large amounts of vitamin A?

Answer. Butter, milk, egg yolk, cod Liver oil

Question 13. What provitamins exist for vitamin A?

Answer: α-, β-, y-Carotenes

Question 14. How many molecules of vitamin A are formed from a single molecule of β-carotene? Answer: Under the action of carotene dioxygenase (carotenase), one molecule of β-carotene is converted into two molecules of vitamin A

Question 15. Which compounds are classified as vitamin A?

Answer: Retinol, retinal, retinoic acid

Question 16. What is the biological role of vitamin A?

Answer. It is involved in scotopic (dim-light) Vision; regulates epithelial differentiation; is essential for stabilizing Cell membranes; affects bone growth, Teeth development, and Spermatogenesis; regulates chondroitin sulfate synthesis; and influences The formation of T- and B-lymphocytes

Question 17. What are the symptoms of vitamin A hypovitaminosis?

Answer: Impaired dim-light vision (night blindness); dryness of the cornea (xerophthalmia); decreased resistance to infections; development of keratitis, Bronchitis, cystitis, etc.

Question 18. Which substance (vitamin) serves as the prosthetic group of rhodopsin?

Answer: Vitamin A (retinol)

Question 19. What are the well-known representatives of Vitamin D Group?

Answer: Vitamin D₂ (ergocalciferol), vitamin D₃ (cholecalciferol)

Question 20. What are the known provitamins of group D?

Answer: 1. Ergosterol — a provitamin of vitamin D₂, found in Fungi and plants

2. 7-Dehydrocholesterol — a provitamin of vitamin D₃, found in animal products

Question 21. Which forms of vitamin D are active?

Answer: Hydroxylated forms

Question 22. Which compounds belong to the active forms of vitamin D₃?

Answer: 1,25(OH)₂D₃ — 1,25-dihydroxycholecalciferol; 24,25(OH)₂D₃ — 24,25-dihydroxycholecalciferol

Question 23. In which Organs does the hydroxylation of vitamin D₃ take place?

Answer: In the liver at the 25th position to form 25(OH)D₃; in the Kidneys — at the 1st or 24th position to form 1,25(OH)₂D₃ or 24,25(OH)₂D₃

Question 24. Which enzyme in the kidneys is involved in the formation of 1,25(OH)₂D₃?

Answer: 1α-Hydroxylase

Question 25. How is The activity of this enzyme regulated?

Answer: 1. Hypocalcemia, hypophosphatemia, and elevated parathyroid hormone levels lead to an increase in 1α-hydroxylase activity

2. An increase in 1,25(OH)₂D₃ levels inhibits 1α-hydroxylase activity and activates the synthesis of 24-hydroxylase, which leads to the formation of 24,25(OH)₂D₃

Question 26. What is the biological role of vitamin D?

Answer: The active forms of vitamin D, acting in concert with Parathyroid hormone and Calcitonin, maintain constant concentrations of calcium and inorganic phosphate in the Blood

Question 27. What is the term for vitamin D hypovitaminosis?

Answer: In children - Rickets, in adults - Osteomalacia

Question 28. What changes are characteristic of hypervitaminosis?

Answer: 1. Calcification of Blood Vessels and soft Tissues of Internal Organs

2. Demineralization of the diaphyses of tubular bones, leading to fractures

3. Enhanced mineralization of the cranial bones and epiphyses of tubular bones in both children and adults

Question 29. Which vitamins belong to the Vitamin K group?

Answer. 1. Vitamin K₁ (phylloquinone), found in plants

2. Vitamin K₂ (menaquinone), found in animal tissues

Question 30. In which biological reactions does vitamin K participate?

Answer: 1. It induces the synthesis of calcium-binding Proteins

2. It serves as a cofactor for γ-glutamyl carboxylase, which facilitates the Formation of γ-carboxyglutamate residues in proteins (such as blood clotting factors II, VII, IX, and X; as well as bone and dentin matrix Gla proteins)

Question 31. How does vitamin K hypovitaminosis manifest?

Answer: Through hemorrhages and prolonged blood clotting times

Question 32. How does vitamin K hypervitaminosis manifest?

Answer: Vascular thrombosis

Question 33. Name a water-soluble analogue of vitamin K.

Answer: Vikasol (Menadione sodium bisulfite)

Question 34. Which substances act as Antivitamins for vitamin K?

Answer: Dicumarol, salicylic acid

Question 35. Which compounds belong to vitamin E?

Answer: α-, β-, γ-Tocopherols. α-Tocopherol is the most widespread and active

Question 36. What is the biological role of vitamin E?

Answer: It acts as an antioxidant, meaning it interrupts the chain reactions of Lipid Peroxidation. Vitamin E performs its antioxidant function in synergy with selenium and Cysteine

Question 37. What are the symptoms of vitamin E deficiency?

Answer: Myopathy and anemia in premature infants

Question 38. What are the symptoms of vitamin E excess?

Answer: Headache, blurred vision

Question 39. Which compounds belong to vitamin F?

Answer: Polyunsaturated Essential Fatty Acids: linoleic, linolenic, and arachidonic acids

Question 40. What is the biological role of polyunsaturated essential fatty acids?

Answer: 1. They are a component of membrane Glycerophospholipids

2. They participate in the formation of esterified Cholesterol in high-density Lipoproteins - HDL (anti-atherogenic effect)

3. Arachidonic acid serves as a precursor for: Prostanoids (Prostaglandins, prostacyclins, thromboxanes) and Leukotrienes

Question 41. Which enzyme catalyzes the synthesis of prostanoids?

Answer: Cyclooxygenase. The activity of this enzyme is inhibited by aspirin and indomethacin

Question 42. What is the biological role of thromboxanes?

Answer: Thromboxanes are produced in platelets. They induce vasoconstriction and platelet aggregation

Question 43. What is the biological role of prostacyclins?

Answer: Prostacyclins are synthesized in the walls of blood vessels and inhibit platelet aggregation

Question 44. What are leukotrienes?

Answer: Leukotrienes are a group of conjugated trienes formed from arachidonic acid via the action of lipoxygenase in leukocytes, platelets, and macrophages

Question 45. What is the biological role of leukotrienes?

Answer: They cause contraction of bronchial smooth Muscle, increase vascular permeability, activate and recruit leukocytes, and regulate inflammatory processes and immediate allergic reactions

Question 46. What is the biological Role of water-soluble vitamins?

Answer: They are part of coenzymes, i.e., non-protein components of Enzymes

Question 47. What is the active form of Vitamin B1?

Answer. Thiamine diphosphate

Question 48. In which reactions does thiamine diphosphate participate?

Answer: In The oxidative decarboxylation of α-keto acids; in the transketolase reaction of the Pentose Phosphate Pathway

Question 49. What are the symptoms of vitamin B₁ deficiency?

Answer: Beriberi disease develops. Signs of polyneuritis, muscular atrophy, lesions of the gastrointestinal tract and Heart muscle appear

Question 50. Which coenzymes are formed from vitamin B₂ (riboflavin)?

Answer: Flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD)

Question 51. In what reactions do FMN and FAD participate?

Answer: In oxidation-reduction reactions

Question 52. What are the signs of vitamin B₂ hypovitaminosis?

Answer: Corneal vascularization, cataract, cheilitis, glossitis, anemia

Question 53. Which coenzymes are formed from Vitamin PP (nicotinamide)?

Answer: Nicotinamide adenine dinucleotide (NAD⁺)

Nicotinamide adenine dinucleotide phosphate (NADP⁺)

Question 54. Which disease is caused by a lack of vitamin PP?

Answer: Pellagra

Question 55. What are the Characteristic Features of pellagra?

Answer: Dementia, dermatitis, diarrhea, mucous membrane lesions, neurological disorders

Question 56. In what reactions does NAD+ participate?

Answer: In oxidation-reduction reactions

Question 57. Which coenzyme is formed from vitamin B₆?

Answer: Pyridoxal phosphate

Question 58. In what reactions does pyridoxal phosphate participate?

Answer: In Transamination, Decarboxylation of amino Acids, and the interconversion of D- and L-Amino Acids

Question 59. Which compound is the active form of folic acid?

Answer: Tetrahydrofolic acid (THFA)

Question 60. In what types of reactions does THFA participate?

Answer: THFA is involved in The transfer of one-carbon units (formyl, methyl, methylene, and methenyl groups)

Question 61. What is the active form of vitamin H (biotin) called?

Answer: Carboxybiotin

Question 62. In what reactions does carboxybiotin participate?

Answer: Carboxylation reactions (e.g., The Biosynthesis of malonyl-CoA from acetyl-CoA)

Question 63. Under what conditions can vitamin H deficiency develop?

Answer: Upon excessive consumption of raw chicken eggs containing the protein Avidin, which irreversibly binds biotin

Question 64. What coenzymes include vitamin B₁₂ in their Structure?

Answer: Vitamin B₁₂ is a component of the coenzymes deoxyadenosylcobalamin and methylcobalamin

Question 65. In what Reactions Involving the conversion of methylmalonyl-CoA to succinyl-CoA, and the synthesis of Methionine from homocysteine

Question 66. What disease develops due to a deficiency of vitamin B₁₂?

Answer: Pernicious (malignant) macrocytic megaloblastic anemia, accompanied by Nervous system disorders and decreased gastric juice acidity

Question 67. In the synthesis of which coenzyme does pantothenic acid participate?

Answer: Coenzyme A

Question 68. What compounds make up coenzyme A?

Answer: 3'-phosphoadenosine-5'-pyrophosphate, pantothenic acid, and thioethylamine

Question 69. What is the biological role of coenzyme A?

Answer: It participates in the activation and transfer of acyl groups (e.g., acetyl-CoA)

Question 70. In what forms does Vitamin C exist?

Answer: Reduced and oxidized forms (dehydroascorbic acid)

Question 71. In what reactions does vitamin C participate?

Answer. Vitamin C acts as a cofactor in the hydroxylation of Lysine and Proline residues during Collagen maturation

Question 72. What is Vitamin C Deficiency called?

Answer: Scurvy

Question 73. What are the symptoms of scurvy?

Answer: Hemorrhages in the Skin and internal organs, limb edema, bleeding Gums, tooth loss, and decreased resistance to infections

Question 74. Vitamin B₂ (riboflavin) is a component of which coenzyme? Answer: Vitamin B₂ is a constituent of flavin enzymes (FAD, FMN) involved in oxidation-reduction reactions

Question 75. Vitamin B₁ (thiamine) is part of which enzymes and in what form?

Answer: In the form of thiamine diphosphate, thiamine is a component of pyruvic and α-ketoglutaric acid Decarboxylases (Pyruvate dehydrogenase complex)

Question 76. Pantothenic acid is a component of which coenzyme?

Answer: Pantothenic acid is a part of coenzyme A (HSKoA), which is involved in the activation of Fatty Acids and amino acids, functioning as An acyl group carrier