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Lec 7 level 4-de (water soluble vitamins)


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Lec 7 level 4-de (water soluble vitamins)

  1. 1. Dental Biochemistry 2 – (Lec. 7)Water soluble vitamins 1
  2. 2. ASCORBIC ACID (VITAMIN C)1. Chemistry of Vitamin C• It is water soluble and is easily destroyed by heat, alkali and storage. In the process of cooking, 70% of vitamin C is lost. The structural formula of ascorbic acid closely resembles that of carbohydrates.• It has strong reducing property 2
  3. 3. 2. Biosynthesis of Ascorbic Acid in Animals• Most animals and plants can synthesize ascorbic acid from glucose. Man cannot synthesize ascorbic acid.3. Excretion of Ascorbic Acid• The vitamin is excreted in urine, Since vitamin C is a strong reducing agent, the Benedicts test will be positive in the urine sample after the vitamin administration. 3
  4. 4. 4. Biochemical Functions ofVitamin C• i. Hydroxylation of proline: Ascorbic acid is necessary for the post-translational hydroxylation of proline and lysine residues. Hydroxyproline and hydroxylysine are essential for the formation of cross-linkings in collagen, which gives the tensile strength of the fibers. This process is absolutely necessary for the normal production of supporting tissues such as osteoid, collagen and intercellular cement substance of capillaries. 4
  5. 5. • ii. Iron metabolism: Ascorbic acid enhances the iron absorption from the intestine. Ascorbic acid reduces ferric iron to ferrous state, which is preferentially absorbed.• iii. Hemoglobin metabolism: It is useful for reconversion of met-hemoglobin to hemoglobin.• iv. Antioxidant property: As an antioxidant, it may prevent cancer formation. 5
  6. 6. 5. Dietary Sources of Vitamin C• Rich sources are lime, lemon and green leafy vegetables.6. Requirement of Vitamin C• Recommended daily allowance (RDA) is 75 mg/day (equal to 50 ml orange juice). During pregnancy,• lactation, and in aged people requirement may be 100 mg/day.7. Therapeutic Use of Vitamin C• Vitamin C has been recommended for treatment of ulcer, trauma, and burns. 6
  7. 7. B COMPLEX GROUP OF VITAMINSThese vitamins are chemically not related toone another. They are grouped togetherbecause all of them function in the cells ascoenzymes. 7
  8. 8. 1- THIAMINE (VITAMIN B1)• Thiamine is also called as vitamin B1.1.Sources• Cereals (whole wheat flour and unpolished rice) are rich sources of thiamine. When the grains are polished, aleurone layer is usually removed. Yeast is also a very good source. 8
  9. 9. 1. Physiological Role of Thiaminei. pyruvate dehydrogenase: The coenzyme form is thiamine pyrophosphate (TPP). It is used in oxidative decarboxylation of alpha keto acids, e.g pyruvate decarboxylase, a component of the pyruvate dehydrogenase complex. It catalyzes the breakdown of pyruvate to acetyl-CoA, and carbon dioxide.ii. Alpha Ketoglutarate dehydrogenase: An analogous biochemical reaction that requires TPP is the oxidative decarboxylation of alpha Ketoglutarate to succinyl CoA and Co2 (TCA cycle). 9
  10. 10. iii.Transketolase in the hexose mono-phosphateshunt pathway of glucose.The main role of thiamine (TPP) is in carbohydrate metabolism. So, the requirement of thiamine is increased along with higher intake of carbohydrates thiamine. Also in case of Polyneuritis that may be associated with pregnancy and old age. 10
  11. 11. • Recommended Daily allowance of thiamine• It depends on calorie intake (0.5 mg/1000 calories).• Requirement is 1-1.5 mg/day.• Thiamine is useful in the treatment of beriberi, alcoholic polyneuritis, neuritis of pregnancy and neuritis of the old age. 11
  12. 12. 2- RIBOFLAVIN (VITAMIN B2)• 1. Structure of Riboflavin• Riboflavin is converted to its active coenzyme forms (FMN & FAD) with the help of ATP. 12
  13. 13. • 2. Coenzyme Activity of Riboflavin• i. Riboflavin exists in tissues bound with enzymes. Enzymes containing riboflavin are called flavoproteins. The two coenzymes are FMN (flavin mononucleotide) and FAD (flavin adenine dinucleotide). The enzyme complex contains molybdenum and iron also.• ii. During the oxidation process, FAD accepts two hydrogen atoms from substrate. In turn, FAD is reduced to FADH2.• iii. FADH2 when oxidized will generate 1.5 ATP molecules. 13
  14. 14. Dietary Sources of Riboflavin• Rich sources are liver, dried yeast, egg and wholemilk.• Good sources are fish, whole cereals, legumes and greenleafy vegetables.Daily Requirement• Riboflavin is concerned mainly with energy metabolism and requirement is related to calorie intake. Adults on sedentary work require about 1.5 mg per day. During pregnancy, lactation and old age, additional 0.2 to 0.4 mg/day are required. 14
  15. 15. 3- NIACIN• Niacin and Nicotinic acid are synonyms. It is also called as pellagra.• The term nicotinic acid is a vitamin; but, nicotine is the potent poison from tobacco.• Niacinamide is the active form of the vitamin, present in tissues. 15
  16. 16. 1.Chemistry of Niacin• The coenzyme forms are Nicotinamide adenine dinucleotide (NAD+) and Nicotinamide adenine dinucleotide phosphate (NADP+)• The nitrogen atom of niacinamide contains one positive charge. The structure is abbreviated as NAD+. (The +ve sign is always shown). In the case of NADP+, one more phosphoric acid is attached to the ribose of the AMP 16
  17. 17. 2. One Hydrogen Atom and OneElectrons i. In the oxidised form, nitrogen of the nicotinamide residue has ahence the oxidized form of coenzyme is usually written as NAD+.ii. In the process of reduction, NAD+ accepts one hydrogen atom fully.The other hydrogen is ionized. Only the electron is accepted. See thepositive sign in the molecule is removed. 2H  H + H+ + e-Thus, NAD+ accepts one H atom and one e- (electron), to form NADH.The hydrogen ion (H+) is released into the surrounding medium. Duringthe oxidation of NADH, the reaction is reversed. 17
  18. 18. 3. NAD+ Dependent Enzymes• One NADH molecule is oxidized in therespiratory chain to generates 2.5 ATPs.4. NADPH Reactions• NADPH is not used for ATP synthesis; it is almost exclusively used for the reductive biosynthesis. 18
  19. 19. 6. Dietary Sources of Niacin• The richest natural sources of niacin are dried yeast, ricepolishing, liver, peanut, whole cereals, legumes, meat andfish. About half of the requirement is met by theconversion of tryptophan to niacin. About 60 mg oftryptophan will yield 1 mg of niacin.9. Recommended Daily Allowance (RDA)• Normal requirement is 20 mg/day. During lactation,additional 5 mg are required. 19
  20. 20. 4- VITAMIN B61. Coenzyme form• Vitamin B6 is the term applied to a family of 3 related pyridine derivatives; pyridoxine (alcohol), pyridoxal (aldehyde) and pyridoxamine.• Active form of pyridoxine is pyridoxal phosphate (PLP). It is synthesized by pyridoxal kinase, ultilizing ATP. 20
  21. 21. 2. Functions of Pyridoxal phosphateThe pyridoxal phosphate (PLP) acts as coenzyme for many reactionsin amino acid metabolism.I. Transamination: These reactions are catalyzed by aminotransferases (transaminases) which employ PLP as the coenzyme• For example, alanine amino transferase Alanine + Alpha keto glutarate  Pyruvate + Glutamic acidII. Decarboxylation: All decarboxylation reactions of amino acidsrequire PLP as coenzyme. A few examples are given below:a. Histidine  histamine, which is the mediator of allergy andanaphylaxis. 21
  22. 22. b. Methionine and cysteine metabolism.c. Heme Synthesis: ALA synthase is a PLPdependent enzyme. This is the rate limiting step inheme biosynthesis. So, in B6 deficiency, anemia iscommon. 22
  23. 23. 3. Production of Niacin: Pyridoxal phosphate isrequired for the synthesis of niacin fromtryptophan (one vitamin is necessary for synthesisof another vitamin)4. Glycogenolysis: Phosphorylase enzyme(glycogen to glucose- 1-phosphate) requires PLP. 23
  24. 24. 1. Dietary Sources• Rich sources are yeast, rich polishing, wheat germs, cereals, legumes (pulses), oil seeds, egg, milk, meat, fish and green leafy vegetables.1. Requirement• Vitamin B6 requirement are related to protein intake and not to calorie intake.• Adults need 1 to 2 mg/day.• During pregnancy and lactation, the requirement is increased 2.5 mg/day. 24
  25. 25. 5- PANTOTHENIC ACID1.Structure• The Greek eor "pantos" means everywhere. As the name suggests, it is widely distributed in nature.• Pantothenic acid contains beta alanine and pantoic acid.• Pantothenic acid and beta mercapto ethanol amine are parts of coenzyme A (CoA). 25
  26. 26. 2. Coenzyme Activity ofPantathenic Acid• The important CoA derivatives are: Acetyl- CoA, Succinyl-CoA• Coenzyme A is an important component of fatty acid synthase complex. The ACP (acyl carrier protein) also contains pantothenic acid. 26
  27. 27. 6- BIOTIN• Biotin acts as co-enzyme for carboxylation reactions. Energy require for carboxylation reactions is provided by ATP. 27
  28. 28. 1. Biotin Requiring Co2 Fixation Reactionsi. Actyl-CoA carboxylase: This enzyme adds Co2 acetyl CoA to form malonyl CoA. This the rate limiting reaction in biosynthesis of fatty acids • Acetyl CoA + Co2 + ATP  Malonyl CoA + ADP + Pii. Propionyl CoA carboxylase • Propionyl CoA + Co2 +ATP  Methyl malonyl CoA + ADP + Pii. Pyruvate carboxylase • Pyuvate + Co2 + ATP  Oxaloacetate + ADP + Pi • This reaction provides the Oxaloacetate, which is the catalyst for TCA cycle. Second, it is important enzyme in the gluconeogenic pathway. 28
  29. 29. 2. Biotin-independent CarboxylationReaction• Carbamoyl phosphate synthetase, which is the stepping stone for urea and pyrimidine synthesis.3. Biotin Antagonists• Avidin, a protein present in egg white has great affinity to biotin. Hence, intake of raw (unboiled) egg may cause biotin deficiency. Biotin was originally named as anti-egg-white-injury-factor. One molecule of avidin can combine with four molecules of biotin. It is curious that egg white contains avidin and egg yolk contains biotin. 29
  30. 30. • 4. Requirement of biotin• About 200-300 mg will meet the daily requirements.• 5. Sources of biotin• Normal bacterial flora of the gut will provide adequate quantities of biotin. Moreover, it is distributed ubiquitously in plant and animal tissues. Liver, yeast, peanut, soybean, ilk, egg yolk are rich source. 30
  31. 31. 7- FOLIC ACID• The latin word folium means leaf of vegetable. Folic acid is abundant in vegetables.1.Chemistry of folic acid • It is composed of three constituents. The pteridine group linked with para amino benzoic acid (PABA) is called pteroic acid. It is then attached to glutamic acid to form pteroyl glutamic acid or folic acid 31
  32. 32. 2. Coenzyme functions of folicacidA.The folic acid is reduced to tetrahydro folic acid (THFA). This is catalyzed by NADPH dependent folate reductase. 32
  33. 33. 3. Sources of folic acid • Rich sources of folate are yeast, green leafy vegetables. Moderate sources are cereals, pulses, oil seeds and egg.4. Recommended daily allowance(RDA) • The requirement of free folate is 200 microgram/day. In pregnancy, the requirement is increased to 400 microgram/day and during lactation to 300 microgram/day. 33
  34. 34. • 5. Folate Antagonists• Solfonamides: They have structural similarity with PABA. Bacteria can synthesize folic acid from the compounds, pteridine, PABA and glutamate. When sulfonamides are given, microorganisms cannot synthesize folic acid and hence their growth is inhibited. Thus, sulphonamides are very good antibacterial agents. Which do not affect the human cells. 34
  35. 35. i. Methotrexate is powerful inhibitor of folate reductase and THFA (tetrahydrofolic acid) generation. Thus these drugs decrease the DNA formation and cell division. It widely used as anticancer drugs, especially for leukemias and choriocarcinomas. 35
  36. 36. 8- VITAMIN B121. Chemistryi. Vitamin B12 is also called as cobalamin, antipernicious anemia factor.ii. Vitamin B12 is water soluble, heat stable and red in color. It contains 4.35% cobalt by weight.iii.It contains one cobalt atom. Four pyrrole rings coordinated with a cobalt atom is called a corrin ring. The 6th valency of the cobalt is satisfied by any of the following groups: cyanide, hydroxyl, adenosyl or methyl. 36
  37. 37. i. Hydroxy cobalamin: when hydroxyl group, it is called hydroxy cobalamin or vitamin B12. Injectable preparations are in this form.ii.Adenosyl cobalamin (Ado-B12): This is the major storage form.iii.Methyl cobalamin: This is the major form seen in blood circulation. The Ado-B12 and methyl B12 are the functional coenzymes. 37
  38. 38. 1.Absorption of vitamin B12i. B12 complex is attached with specific receptors on mucosal cells. The whole B12 complex is internalized.2. Functional Role of B12i. Methyl malonyl CoA isomerase: During the metabolism of odd chain fatty acids, the propionyl CoA is carboxylated to methyl malonyl CoA. It is then isomerized by methyl malonyl isomerase or mutase (containing Ado-B12) to succinyl CoA, which enters into citric acid cycle. In B12 deficiency, methyl malonyl CoA is excreted in urine ( methyl malonic aciduria). 38
  39. 39. 3. Requirement of vitamin B12 • Normal daily requirement is 1-2 microgram/day. During pregnancy and laction, this is increased to 2 microgram/day.4. Dietary sources • Liver is the richest source. Curd is a good source, because lactobacillus can synthesize B12 39