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**