FA-Biochem-Nutrition USMLE Step 1
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23 terms
Terms | Definitions |
|---|---|
 Fat soluble vitamins and basic functions | Vitamin A - vision Vitamin D - bone calcification, calcium homeostasis Vitamin E - antioxidant Vitamin K - clotting factors Absorption dependent on ileum and pancreas Toxicity more common than water soluble vitamins because of accumulation in fat Malabsorption syndromes (steatorrhea) can cause fat-soluble vitamin deficiencies |
| Water soluble vitamins and vasic functions | Vitamin B 1,2,3,5,6,7 & folate (blood and neural development), cobalamin (blood, CNS) Vitamin C - collagen synthesis and antioxidant All wash out easily from body except folate and cobalamin (stored in liver) |
| Vitamin A | Retinol - antioxidant, visual pigment Essential for normal differentiation of epithelial cells into specialized tissue Deficiency - night blindness, dry skin Excess - fatigue, headache, skin changes, sore throat, alopecia, arthralgia (joint pain), teratogenic |
| Vitamin B1 | Thiamine Thiamine pyrophosphate is a cofactor for metabolic enzymes, including pyruvate dehydrogenase (glycolysis), alpha-ketoglutarate dehydrogenase (TCA cycle), transketolase (pentose phosphate shunt), branched-chain AA dehydrogenase |
| Vitamin B1 deficiency | Impaired glucose breakdown, ATP depletion, brain and heart affected first Leads to Wernicke-Korsakoff syndrome and beri-beri (also seen secondary to malnutrition and malabsorption) Wernicke-Korsakoff - confusion, ophthalmoplegia, ataxia, confabulation, memory loss, damage to mamillary bodies, dorsomedial nucleus of thalamus |
| Beri-Beri | Due to vitamin B1 deficiency or malnutrition/malabsorption Dry beri-beri: polyneuritis, symmetrical muscle wasting Wet beri-beri: high-output cardiac failure, edema |
| Vitamin B2 | Riboflavin (FAD, FMN) Deficiency leads to cheilosis (inflammation of lips, scaling and fissures at corners of mouth) and corneal vascularization |
| Vitamin B3 | Niacin (constituent of NAD, NADP) - derived from tryptophan Synthesis requires vitamin B6 Deficiency - glossitis, if severe pellagra (dermatitis, diarrhea, dementia).can be caused by Hartnup disease (decrased tryptophan absorption), malignant carcinoid syndrome (increased tryptophan metabolism), or isoniazid (decreased vitamin B6 levels) |
| Vitamin B5 | Pantothenate - essential component of CoA and fatty acid synthase Deficiency - dermatitis, enteritis, alopecia, adrenal insufficiency |
| Vitamin B6 | Pyridoxine Pyridoxal phosphate - cofactor used in transamination (ALT, AST), decarboxylation, glycogen phosphorylase, cystathione synthesis, heme synthesis Required for synthesis of niacin (B3) from tryptophan Deficiency - convulsions, hyperirritability, peripheral neuropathy, sideroblastic anemia |
| Vitamin B12 | Cobalamin - cofactor for homocysteine methyltransferase (homocysteine -> methionine) and methylmalonyl CoA mutase Deficiency leads to macrocytic, megablastic anemia, neurologic symptoms (paresthesia, subacute combined degeneration) Large reserve pool exists in the liver, found in animal products Deficiency due to malabsorption, lack of intrinsic factor, absence of terminal ileum |
| Folic acid | Vitamin B9 Converted into THF (tetrahydrofolate) - cofactor used in 1-carbon transfer/methylation reactions Important for synthesis of nucleic acids Deficiency - macrocytic, megablastic anemia, no neurologic symptoms Deficiency is common and could be due to alcoholism and pregnancy Small reserve pool in liver, found in green leaves Supplemental folic acid in early pregnancy can reduce neural tube defects |
| SAM | S-adenosyl methionine ATP+methionine -> SAM SAM transfers methyl units Regeneration of methionine and SAM dependent on vitamin B12 and folate Required for conversation of NE -> epinephrine |
| Biotin | Vitamin B9 - cofactor for carboxylation enzymes (addition of one carbon group) - pyruvate carboxylase, acetyl CoA carboxylase, propionyl-CoA carboxylase Deficiency - rare, but high avidin intake can cause it - dermatitis, enteritis, alopecia |
| Vitamin C | Ascorbic acid - found in fruits and vegetables Facilitate iron absorption by keeping iron in Fe2+ reduced state Necessary for hydroxylation of proline and lysine residues for collagen synthesis Necessary for dopamine B-hydroxylase (dopamine -> NE) Deficiency - scurvy (swollen gums, bruising, hemiarthrosis, anemia, poor wound healing), weakened immune response |
| Vitamin D | Ergocalciferol (D2) - found in plant products Cholecalciferol (D3) - found in milk and synthesized by sun-exposed skin 25-OH D3 - storage form; 1,25-OH2 D3 (calcitriol) - active form Facilitates intestinal absorption of calcium and phosphate, increases bone resorption Deficiency - rickets/osteomalacia, hypocalcemic tetany Breastfed babies need vitamin D supplementation Excess - hypercalcemia, loss of appetite, stupor |
| Vitamin E | Antioxidant - protects erythrocytes and membranes from free-radical damage Deficiency leads to hemolytic anemia, muscle weakness, posterior column and spinocerebellar tract demyelination |
| Vitamin K | Catalyzes gamma-carboxylation of glutamic acid residues on proteins involved in blood clotting Necessary for synthesis of clotting factors II, VII, IX, X and protein C and S Synthesized by intestinal flora Warfarin is a vitamin K antagonist Deficiency - neonatal hemorrhage due to sterile intestine at birth or use of broad-spectrum antibiotics |
| Zinc | Essential for activity of many enzymes Important in the formation of zinc fingers Deficiency - wound healing, hypogonadism, decreased adult hair, dysgeusia, anosmia |
| Ethanol metabolism | Ethanol -> acetaldehyde via alcohol dehydrogenase Acetaldehyde -> acetate via aldehyde dehydrogenase Both steps require reduction of NAD to NADH NAD+ is the limiting reagent Alcohol dehydrogenase operates via zero-order kinetics |
| Drugs that alter alcohol metabolism | Formepizole - inhibits alcohol dehydrogenase and is an antidote for methanol or ethylene glycol poisoning Disulfiram - inhibits acetaldehyde dehydrogenase; accumulation of acetaldehyde leads to hangover symptoms |
| Ethanol hypoglycemia | High ethanol consumption and metabolism increases NADH/NAD+ ratio in liver Leads to conversion of pyruvate -> lactate, oxaloacetate -> malate to regenerate NAD+ Inhibits gluconeogenesis and stimulates fatty acid synthesis Leads to hypoglycemia and hepatic fatty change commonly seen in chronic alcoholics |
| Kwashikor vs. marasmus | Kwashikor - protein malnutrition resulting in skin lesions, anemia, edema, liver malfunction (child with swollen belly) Marasmus - energy malnutrition resulting in tissue and muscle wasting, loss of subcutaneous fat, and variable edema |
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