Vitamins and Minerals II Flashcards Preview

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Flashcards in Vitamins and Minerals II Deck (29)
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describe vitamin E and its function

  • alpha tocopherol is the most active form
  • vitamin E functions as a lipid soluble antioxidant in cell membranes
    • prevents perioxidation of membrane lipids
    • prevents formation of oxidized LDL 
    • scavenges free radicals


name the 3 antioxidant vitamins

vitamin C, vitamin E and beta-carotene



describe vitamin E deficiency

  • hemolytic anemia (abnormal cellular membranes)
  • reduces deep tendon reflexes and gait problems due to axonal degeneration


describe function and deficiency of vit. K

  • required as coenzyme for post-translational modification (gamma-carboxylation) of various clotting factors 
    • II, VII, IX and X
    • proteins C and S 
  • also synthesized by intestinal bacteria therefore broad spectrum antibiotics is a risk factor for deficiency
  • vit. K stored in the least amount among fat soluble vitamins therefore deficiency is the earliest to manifest


describe gamma carboxylation and role of vit K

  • gamma-carboxylation of the clotting factors II, VII, IX and X occurs in the liver to form mature clotting factors 
  • vit. K is converted from the hydroquinone form to the epoxide form
  • warfarin prevents regeneration of hydroquinone form of vit. K
    • increased prothrombin/INR time


describe functions of vitamin C (ascorbic acid)

  • required for the maintenance of normal CT (collagen synthesis) and wound healing
    • vit. C acts as a coenzyme for hydroxylation of proline and lysine residues in collagen (prolyl and lysyl hydroxylase): facilitates formation of H-bonds
  • required for absorption of iron: reduces iron to the ferrous state in the stomach which facilitates absorption of iron
  • water soluble anti-oxidant


what are earliest signs of vit. C deficiency?

perifollicular hemorrhage


name the enzymes requiring vitamin B1 (thiamine) as a coenzyme

  • coenzyme form = TPP (thiamine pyrophosphate)
    • pyruvate dehydrogenase
    • alpha-KG dehydrogenase
    • branched chain alpha-keto acid dehydrogenase
    • transketolase in the PPP


describe thiamine deficiency

  • beriberi
    • common when rice is the major diet component
    • affects highly aerobic tissues (brain + cardiac)
    • polyneuropathy: disruption of motor, sensory and reflex arcs which could progress to paralysis (dry beriberi)
    • cardiovascular symptoms = cardiac failure (wet beriberi)


explain what a lab test for thiamine deficiency would show

  • low erythrocyte transketolase activity and increased activity on addition of TPP


describe Wernicke-Korsakoff syndrome

  • thiamine deficiency
  • associated with chronic alcoholism 
  • ophthalmoplegia and nystagmus 
  • ataxia, confusion, disorientation and loss of memory


describe use of vitamin B2 (riboflavin) in reactions

  • coenzyme forms:
    • flavin mononucleotide (FMN)
    • flavin dinucleotide (FAD)
  • found in oxidation-reduction reactions:
    • TCA cycle: succinate dehydrogenase, PDH
    • beta-oxidation: acyl CoA DH


describe riboflavin deficiency

  • nutritional 
  • signs and symptoms:
    • cheilosis: areas of pallor, cracks and fissures at the angles of the mouth
    • glossitis: inflammation and atrophy of the tongue
    • facial dermatitis


describe function of vitamin B3 (niacin) and therapeutic use

  • coenzyme forms:
    • NAD+
    • NADP+
  • act as coenzymes in oxidation-reduction reactions
    • NAD: dehydrogenases
    • NADP: reactions in the HMP shunt and fatty acid and cholesterol synthesis (HMG CoA reductase)
  • therapeutic use: niacin inhibits lipolysis in the adipose tissue and greatly reduces production of free fatty acids; treatment of type IIb hyperlipoproteinemia


describe niacin deficiency

  • Pellagra (4 D's)
    • dermatitis
    • diarrhea
    • dementia
      • loss of memory
    • death


explain how tryptophan is related to niacin/pellagra

  • tryptophan can be used to synthesize NAD+ and NADP+
  • corn based diets can cause pellagra 
  • patients with Hartnup disease can have pellagra
    • need supplementation of dietary niacin
  • patients with carcinoid syndrome since there is excessive conversion of tryptophan to serotonin
    • less availability of trpytophan for NAD formation 


describe function of biotin

  • biotin is the prosthetic group for most carboxylation reactions
    • pyruvate carboxylase
    • acetyl-CoA carboxylase
    • propionyl CoA carboxylase
  • avidin, present in raw egg whites, inhibits absorption of biotin


describe functions of vitamin B6 (pyridoxine)

  • serves as precursors for PLP, which acts as a coenzyme for:
    • transamination 
    • amino acid decarboxylation (neurotransmitter synthesis)
    • condensation (ALA synthase in heme synthesis)
    • glycogen phosphorylase
    • conversion of homocysteine to cysteine
      • many children with homocystinuria respond to B6 supplementation


name the reactions that require PLP as a coenzyme


describe how isoniazid therapy can affect pyridoxine

  • administration of isoniazid (anti-TB drug):
    • inactivates pyridoxine
    • pyridoxine supplements are given as a part of anti-TB regimens
    • peripheral neuropathy is observed as an adverse effect when pyridoxine supplements are not given with isoniazid therapy


describe effects of pyridoxine deficiency

  • microcytic anemia: reduced heme synthesis as a result of reduced ALA synthase activity
  • peripheral neuropathy: due to reduced neurotransmitter formation
    • seizures may also occur
  • increased risk of cardiovascular disease (high levels of plasma homocysteine)


describe the function of vitamin B12 (cobalamin) in the synthesis of methionine

  • required as a coenzyme for 2 reactions:
    • synthesis of methionine (methionine synthase)
  • this step also converts methyl-THF to THF; THF is the active form of folic acid 
    • if there is vit. B12 deficiency, folate is trapped as methyl-THF (folate trap) which results in macrocytic anemia 


describe the function of vit. B12 (cobalamin) in the isomerization of methylmalonyl CoA

  • in vit. B12 deficiency, serum methylmalonate levels are high
    • high methylmalonate levels may be responsible for the neurological manifestations of vit. B12 deficiency
    • dietary vit. B12 supplementation is useful in patients with inherited methylmalonic aciduria


describe causes of vit. B12 deficiency

  • vit. B12 is not present in plants and is derived from animal foods; vegans have high risk of developing deficiency
  • intrinsic factor (IF) produced by the gastric parietal cells is essential for vit. B12 absorption
    • parietal cell destruction = lack of IF, which leads to pernicious anemia
    • IF-B12 complex is absorbed in the terminal ileum


describe the functions of folic acid

  • key role in 1-C metabolism
  • THF receives 1-C from ser, gly, his and transfers them to intermediates in purine and pyrimidine nucleotide synthesis 
  • most cells receive folate in the form of methyl-THF; the conversion of methyl-THF to THF requires vit. B12
    • otherwise, folate trapping


describe manifestations of folic acid deficiency


how to differentiate between folic and and B12 deficiency?

both have elevated homocysteine levels but only B12 deficiency has increased methylmalonate levels as well


there is an increased risk of _______ in the fetus with folic acid deficiency

there is an increased risk of neural tube defects in the fetus with folic acid deficiency

folic acid supplements are recommended for all women at the time of conception and during the 1st trimester