Vitamins Flashcards
1
Q
Vitamin B1 (Thiamine)
A
- Found in grains, meats, legumes.
- Biologically active form: Thiamine Pyrophosphate (TPP).
- Functions of TPP: 1) Transketolation reactions in Pentose Phosphate Pathway 2) Conversion of pyruvate to acetyl-CoA 3) Conversion of alpha-ketoglutarate to succinyl-CoA (TCA cycle) 4) Creation of branched chain aa’s (isoleucine, leucine, valine).
- Deficiency: 1) Muscle cramps, 2) Paresthesias, 3) Irritability, 4) Beriberi (wet involves cardio system, dry involves nervous system).
- Wet Beriberi (brought on by physical exertion & increased carb intake): Neuropathy & Heart Failure. Includes triad of Peripheral vasodilation, biventricular failure, and edema.
- Dry Beriberi (with little physical exertion & lower caloric intake): Involves Wernicke-Korsakoff syndrome which occurs in chronic alcoholics with thiamine deficiency. Wernicke’s encephalopathy triad: ophthalmoplegia, truncal ataxia, confusion. If untreated, this progresses to Korsakoff syndrome which involves impaired short-term memory and confabulation.
2
Q
Vitamin B2 (Riboflavin)
A
- Found in milk and other dairy products.
- Serves as precursor for coenzymes: Flavin Mononucleotide (FMN) & Falvin Adenine Donucleotide (FAD).
- FMN & FAD involved in many oxidation-reduction reactions.
- Functions: 1) Metabolism (FA oxidation, AA oxidation, TCA cycle), 2) Conversion of Tryptophan to Niacin, 3) Erythrocyte Integrity through erythrocyte glutathione reductase.
- Deficiency: 1) 2 C’s (Cheilosis, Corneal Vascularization), 2) Glossitis, 3) Anemia secondary to RBC lysis.
3
Q
Vitamin B3 (Niacin)
A
- Found in liver, milk, unrefined grains. Also converted in body from tryptophan.
- Niacin (aka nicotinic acid) required for formation of: Nicotinamide Adenine Dinucleotide (NAD+) & Nicotinamide Adenine Dinucleotide Phosphate (NADP+).
- Function: NAD+ & NADP+ convert to NADH & NADPH, which are soluble electron carriers and involved in many oxidation-reduction reactions.
- Deficiency: Niacin deficiency referred to as Pellegra and associated with 3 D’s, dermatitis, diarrhea, dementia.
4
Q
Vitamin B5 (Pantothenic Acid)
A
- Found in most foods.
- Pantothenic acid is major component of CoA
- Function: CoA is a coenzyme in the transfer of acyl groups in reactions of TCA cycle, FA oxidation, acetylations, and cholesterol synthesis.
- Deficiency: Rare, but may cause: 1) Paresthesias, 2) Dysesthesias, 3) GI distress.
5
Q
Vitamin B6 (Pyridoxine)
A
- Found in wheat, egg yolk, meats.
- Pyridoxine serves as building block for Pyridoxal Phosphate (PLP).
- Function: PLP involved in AA metabolism. PLP is prosthetic group on all aminotransferases and creates AST, ALT. PLP involved in: 1) transamination, 2) deamination, 3) decarboxylation, 4) condensation rxns.
- Deficiency: Typically associated with pediatric malnutrition or after use of oral contraceptives, isoniazid, cycloserine, penicillamine. Deficiency causes: 1) seizures/convulsions, 2) hyperirritability, 3) angular cheilitis.
6
Q
Vitamin B12 (Cobalamin)
A
- Note: B12 & Folic Acid very interlinked*
- Found in animal products (meat or dairy).
- Absorption: B12 binds Intrinsic Factor (IF, secreted by parietal cells) in stomach and then absorbed ileum. B12 binds “transcobalamin II” in circulation until it arrives at liver.
- Function: Cofactor in 2 major enzymes: 1) Methionine Synthase, 2) Methylmalonyl-CoA mutase (FA metabolism).
- Methionine Synthase: Catalyzes formation of methionine from homocysteine via a one-carbon transfer from methyl-THF (Note folic acid presence), which then turns into THF.
- Deficiency: Deficiency of B12 causes buildup of methyl-THF in cell, which eventually leaves cell and causes secondary Folic Acid deficiency. B12 deficiency leads to 1) Megaloblastic Anemia (MCV>100fL & hypersegmented neutrophils), which is often caused by pernicious anemia (autoimmune attack on gastric parietal cells leading to decreased Intrinsic Factor and hence decreased B12 absorption).
- Note: Magaloblastic changes from B12 deficiency indistinguishable from Folic Acid deficiency. However, only B12 deficiency causes Neuropathy.
7
Q
Folic Acid
A
- Note: B12 & Folic Acid very interlinked*
- Found in fruits, vegetables.
- Functions (mainly 1-carbon transfers): 1) Conversion of Homocysteine to Methionine (B12 is cofactor) (Note: Methyl-trap hypothesis, where methyl-THF can only donate its carbon to homocysteine, which will form methionine, and methyl-THF will turn into THF. Hence, if B12 deficiency, then methyl-THF trapped), 2) Conversion of Serine to Glycine (B6 is cofactor), 3) Conversion of dUMP to dTMP, 4) Purine ring formation.
- Deficiency: Leads to 1) Megaloblastic Anemia
- Methotrexate blocks conversion of DHF into THF by inhibiting the enzyme Dihydrofolate reductase (DHFR). This blocks DNA synthesis.
- Note: Magaloblastic changes from B12 deficiency indistinguishable from Folic Acid deficiency. However, only B12 deficiency causes Neuropathy.
8
Q
Biotin
A
- Found in peanuts, cashews, almonds, etc.
- Biotin is a coenzyme involved in many carboxylation reactions (“professional carboxylator”) through carrying activated CO2.
- Function: 1) Conversion of pyruvate to oxaloacetate, 2) Conversion of propionyl-CoA to methylmalonyl-CoA in synthesis of odd-chain FAs.
- Deficiency: Rare since intestinal flora produce adequate levels.
9
Q
Vitamin C (Ascorbic Acid)
A
- Found in citrus fruits.
- Function: 1) Specific antioxidant required in formation of many hydroxylases. For example, proline and lysine hydroxylases that hydroxy-modify amino acids, hydroxyproline and hydroxylysine, involved in collagen synthesis, 2) Increases iron absorption.
- Deficiency: Scurvy, due to unstable collagen triple helix formation. Tissues with high collagen turnover most affected. Includes bleeding gums, easy bruising, slow wound healing, anemia, osteoporosis.
10
Q
Vitamin A (Retinol)
A
- Found in fish oils, meats, dairy products, eggs.
- Functions: 1) Form called “Retinal” combines with opsin in eye to form rhodopsin which is critical for light detection and vision, 2) Form called “Retinoic acid” is a ligand for nuclear hormone receptors in epithelial cells in respiratory tract, skin, cornea, conjunctiva, and other tissues involved in their proliferation and differentiation.
- Deficiency: 1) Visual problems including night blindness, xerophthalmia, hyperkeratosis, anemia, bitot spots, keratomalacia. 2) Disorders of epithelial cell differentiation and proliferation as well as frequent respiratory infections secondary to respiratory epithelial defects. 3) Impaired Immunity as in “Acute Promyelocytic Leukemia (APL)”.
- Overdose/Toxicity: Acutely can cause nausea, vertigo, blurry vision. Chronically can cause ataxia, alopecia, hyperlipidemia, hepatotoxicity. Also, high Vitamin A levels in first trimester of pregnancy are teratogenic and can lead to fetal loss.
11
Q
Vitamin D (Cholecalciferol)
A
- Obtained from sunlight or diet.
- Ultimate job of Vitamin D is Calcium homeostasis.
- UV light causes 7-dehydrocholesterol in skin to convert into Cholecalciferol (D3). In liver, D3 converted into 25-OH D3. In kidney, 25-OH D3 converted into 1,25-OH D3 (calcitriol, active form of vitamin D) or 24,25-OH D3 (inactive form).
- Calcitriol increases calcium absorption in intestine, reabsorption in kidneys, and resorption in bone.
- Overall Calcium Homeostasis: Low calcium levels cause PTH release which increases calcitriol which then has negative feedback loop on PTH. Conversely, high calcium levels inhibit PTH production.
- Deficiency: 1) Rickets in children, 2) Osteomalacia in adults. Both due to decreased bone mineralization.
- Overdose/Toxicity: Hypercalcemia causes kidney stones (renal failure), dementia, constipation, abdominal pain, depression, anorexia, polyuria.
12
Q
Vitamin E (alpha-tocopherol)
A
- Found in sunflower oil, corn oil, soybeans, meats, fruits, vegetables.
- Function: Found in cell membranes and serves as antioxidant that protects from radicals formed by peroxidation of FAs.
- Deficiency: Rare, but causes 1) Hemolytic Anemia, 2) Peripheral Neuropathy, 3) Ophthalmoplegia.
- Overdose/Toxicity: Interferes with Vitamin K metabolism at high levels.
13
Q
Vitamin K (Phylloquinone)
A
- Found in vegetable/animal sources (phylloquinone) and also made by intestinal flora (menaquinone).
- Function: Vitamin K carboxylates glutamate residues on clotting factors prothrombin (factor II), and factors VII, IX, and X to form gamma-carboxyglutamate. This modification necessary for maturation and function of the clotting factors.
- Warfarin (Anticoagulant): In converting the glutamate residues to gamma-carboxyglutamates, the vitamin K gets oxidized to its epoxide form. This epoxide form is converted back to the reduced active Vitamin K form through the enzyme VKOR (Vitamin K Epoxide Reductase). However, warfarin blocks VKOR and hence causes anti-coagulation downstream.
- Deficiency: Rare since intestinal flora produce it. However, symptoms similar to anti-coagulation.
- Overdose/Toxicity: Can cause 1) allergic reactions, 2) hemolytic anemia, 3) hepatotoxicity.
14
Q
Water Soluble Vitamins
A
- Vitamin B’s (B1, B2. B3, B5, B6, B12).
- Vitamin C
- Folic Acid
- Biotin
*Note: Usually associated with deficiencies since easily excreted by kidneys.
15
Q
Fat Soluble Vitamins
A
- Vitamin A
- Vitamin D
- Vitamin E
- Vitamin K
*Note: Deficiencies rare. However, toxicities more common since they cannot be easily secreted.
