Vitamins and Minerals II

Question 1

describe vitamin E and its function

Answer 1

• 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

Question 2

name the 3 antioxidant vitamins

Answer 2

vitamin C, vitamin E and beta-carotene

Question 4

describe vitamin E deficiency

Answer 4

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

Question 5

describe function and deficiency of vit. K

Answer 5

• 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

Question 6

describe gamma carboxylation and role of vit K

Answer 6

• 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

Question 7

describe functions of vitamin C (ascorbic acid)

Answer 7

• 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

Question 8

what are earliest signs of vit. C deficiency?

Answer 8

perifollicular hemorrhage

Question 9

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

Answer 9

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

Question 10

describe thiamine deficiency

Answer 10

• 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)

Question 11

explain what a lab test for thiamine deficiency would show

Answer 11

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

Question 12

describe Wernicke-Korsakoff syndrome

Answer 12

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

Question 13

describe use of vitamin B2 (riboflavin) in reactions

Answer 13

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

Question 14

describe riboflavin deficiency

Answer 14

• 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

Question 15

describe function of vitamin B3 (niacin) and therapeutic use

Answer 15

• 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

Question 16

describe niacin deficiency

Answer 16

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

Question 17

explain how tryptophan is related to niacin/pellagra

Answer 17

• 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

Question 18

describe function of biotin

Answer 18

• 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

Question 19

describe functions of vitamin B6 (pyridoxine)

Answer 19

• 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

Question 20

name the reactions that require PLP as a coenzyme

Answer 20

Question 21

describe how isoniazid therapy can affect pyridoxine

Answer 21

• 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

Question 22

describe effects of pyridoxine deficiency

Answer 22

• 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)

Question 23

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

Answer 23

• 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

Question 24

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

Answer 24

• 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

Question 25

describe causes of vit. B12 deficiency

Answer 25

• 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

Question 26

describe the functions of folic acid

Answer 26

• 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

Question 27

describe manifestations of folic acid deficiency

Answer 27

Question 28

how to differentiate between folic and and B12 deficiency?

Answer 28

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

Question 29

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

Answer 29

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