Vitamins Structure & Function PDF

Structure & Function of Vitamins 1 Recommended Dietary Allowance (RDA) 2  Vitamins - Introduction  Organic compounds required in the diet in small amounts  Classed as fat soluble (A, D, E and K) or water soluble (C and the B complex)  In consid...

Structure & Function of Vitamins 1 Recommended Dietary Allowance (RDA) 2  Vitamins - Introduction  Organic compounds required in the diet in small amounts  Classed as fat soluble (A, D, E and K) or water soluble (C and the B complex)  In considering the different vitamins we shall review: Chemical nature Function Consequences of deficiency 3  Vitamin A  Function: Vitamin A/Retinol is a precursor for retinal (used in the visual cycle) and for retinoic acid (required for epithelial cells’ maintenance)  Effect of Deficiency: Night blindness & keratinization of epithelial cells  Oral manifestations: gingivitis, periodontitis  Sources: orange and yellow vegetables, eggs, fish liver oil. 4  Vitamin A - types  All compounds with Vitamin A activity are called Retinoids  Three # compounds: Retinol, Retinal, Retinoic acid β-carotene is a precursor of retinol 5 Vitamin A deficiency – Gingivitis & Periodontitis 6  Thiamine  Function: Thiamine is converted to thiamine pyrophosphate (Vitamin B1) which is an important cofactor in converting carbohydrates into energy and maintains proper cardiac, muscle, and nervous functions  Effect of Deficiency: Beriberi and Wernicke-Korsakoff syndrome, Polyneuritis, cardiac pathology, edema  Oral manifestations: Satin like appearance of tongue (red, smooth, sore tongue), angular cheilitis  Sources: beef, beans, nuts, bananas, green peas, etc.  RDA: 1.5 mg/day 7 Conversion of Thiamine to TPP 8  Thiamine deficiency - Symptoms  Wet beriberi affects the CVS - shortness of breath, increased heart rate, swelling of legs  Dry beriberi affects the nervous system - numbness in hands & feet, difficulty walking, pain, confusion & vomiting  Wernicke-Korsakoff syndrome (WKS) affects the nervous system - anterograde amnesia, hallucinations/confusion, 9  Riboflavin Xerostomia  Function: Riboflavin (Vitamin B2) is a precursor for the coenzymes, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) used to oxidize substrates  Effect of Deficiency: atrophy of filiform papillae,  angular cheilitis  Sources: Milk, liver, eggs, cereals, green leafy vegetables, etc. 10 Riboflavin – FMN & FAD synthesis 11  Niacin – Nicotinic acid  Function: As nicotinic acid or nicotinamide it is a precursor for the NAD and NADP (coenzymes for dehydrogenases)  Effect of Deficiency: Pellagra (dermatitis, diarrhea, dementia and if severe, death)  Oral manifestations: Angular cheilosis, glossitis, ulcerative glossitis  Sources: Legumes, meat 12 Niacin – NAD & NADP synthesis 13  Pyridoxine – Vitamin B6  Function: Pyridoxine (pyridoxal) is a precursor of the coenzyme pyridoxal phosphate – for enzymes catalyzing transamination, deamination, decarboxylation and for glycogen phosphorylase  Effect of Deficiency: Dermatitis (skin inflammation), convulsions, microcytic anemia (fatigue, tiredness, shortness of breath, dizziness) 14 Pyridoxine – Vitamin B6 15  Biotin  Function: coenzyme in ATP-dependent carboxylation rxns & covalently bound to enzyme through linkage with the amide side chain of lysine  Effect of Deficiency: Dermatitis, anorexia, nausea, muscle pain  Sources: Intestinal µ-organisms, liver, 16  Biotin/lysine interaction  The biotin has a 5C side chain  Terminal carboxyl is in amide linkage to the amino group of an enzyme lysine  The biotin & lysine side chains form a long swinging arm that allows the biotin ring to swing back & forth between 2 active sites  Pyruvate Carboxylase uses biotin as prosthetic group 17  Pantothenic Acid  Function: Pantothenic acid (Vitamin B5) is a precursor of pantotheine. This structure forms part of coenzyme A  Effect of Deficiency: A deficiency is practically unknown. There may be nausea and fatigue  Sources: Pantothenic acid is widely distributed and is synthesized by some intestinal bacteria  RDA: An RDA has not been established. 5-10 mg/ day might 18 Pantothenic Acid & Coenzyme A structure 19  Folic Acid  Function: Vitamin B9 is a precursor for tetrahydrofolate - used as a primary source of one carbon unit during oxidation rxns  Effect of Deficiency: Megaloblastic anemia, GI disturbances  Sources: Intestinal bacteria, liver, yeast and green 20 Folic Acid & Tetrahydrofolate (THF) Site of attachment of 1C units 21  Tetrahydrofolate & Carbon transfer The formaldehyde released by serine cleavage is captured immediately by THF while still within the active site of the serine hydroxymethyltransferase 22  Vitamin B12 - Cobalamin  Chemical Nature: Vitamin B12 is a complex multiple ring structure which includes a cobalt atom (cobalamin)  Function: Vitamin B12-derived cofactors are used for 2 rxns: Rearrangement reaction - conversion of Methylmalonyl CoA to succinyl-CoA by methylmalonyl-CoA isomerase/mutase (deoxyadenosyl cobalamin is the coenzyme) Methylation reaction - conversion of homocysteine to 23 Vitamin B12 - Cobalamin 24 Cobalamin-derived cofactors methionine synthase deoxyadenosyl cobalamin is the methyl cobalamin is the coenzyme coenzyme 25  Vitamin B12 - Cobalamin  Vitamin B12 is absorbed from the ileum as a complex with intrinsic factor which is produced by the gastric mucosa  Effect of Deficiency: Pernicious anemia and degeneration of spinal cord neurons  Oral manifestations: Angular cheilosis, hemorrhagic gingiva, halitosis (chronic bad breath), detachment of periodontal fibers 26 Periodontal ligaments detachment 27  Vitamin C – Ascorbic Acid  Function: A water soluble antioxidant promoting the hydroxylation of proline & lysine residues of collagen. It is also required in the synthesis of dopamine and bile acids  Effect of Deficiency: Scurvy (hemorrhage, impaired wound healing and bone formation)  Oral manifestations: Bleeding gums, loose teeth  Sources: Fruits and vegetables  RDA: 60 mg/day 28 Vitamin C – structure & function Ascorbate acts as a reducing agent to convert the oxidized iron atom (Fe3+) back to its reduced state (Fe2+) in the enzyme prolyl hydrxylase 29  Vitamin D  Function: Regulation of calcium levels through actions on intestine, kidney and bone.  Vitamin D3 (cholecalciferol) requires conversion to 1,25- dihydroxy vitamin D3 to form the active compound  Effect of Deficiency: Rickets, osteomalacia (softening of the bones)  Oral manifestations: Deficiency associated with incomplete mineralization of teeth. Excess associated with pulp calcification  Sources: UV irradiation of 7-dehydrocholesterol in the skin, fish liver oils and supplemented milk  RDA: 600 international units (15 µg cholecalciferol) 30 Vitamin D synthesis 31 Vitamin D deficiency - Rickets & Osteomalacia 32  Vitamin E  Function: Vitamin E (Tocopherol) is a lipid-soluble antioxidant and helps to prevent lipid damage  Effect of Deficiency: deficiency is associated with lysis of erythrocytes  Sources: Vegetables and wheat germ oil  RDA: 15 international unit 33 Vitamin E – structure 34  Vitamin K  Function: Vitamin K is a coenzyme for the carboxylation of Glu side chains of some blood clotting factors (prothrombin, factors VII, IX and X)  Effect of Deficiency: rare but can be associated with prolonged blood clotting times  Oral manifestation: gingival bleeding  Sources: Vitamin K is produced by intestinal bacteria.  RDA: 70-140 µg may be appropriate. 35 Vitamin K – Glutamate carboxylation 36 Vitamin K – Blood clotting & Warfarin 37  The End… 38