Vitamins

Question 1

Water Soluble Vitamins

Answer 1

• Low storage
• Low toxicity
• Thiamin, Riboflavin, Niacin, Pantothenic Acid, Pyridoxine, Biotin, Folic Acid, Cobalamin, Ascorbic Acid

Question 2

Vitamin B₁ (Thiamin) - Energy (Carbonyl Groups)

Answer 2

• Main Functions:
  
  • Oxidative decarboxylation reactions
    
    • Pyruvate kinase, a-ketogluterate dehydrogenase, a-ketoacid dehydrogenase
  • Transketolase reactions
    
    • Hexose monophosphate shunt
• Dietary necessity for:
  
  • All animals (interesting: cats need ~3x as much as dogs)
• Deficiency usually presents as weakness, neuropathy, and/or CNS disorders - fatal if untreated
  
  • Beriberi (primates)
  • Polioencephalomalacia (cats/ruminants)
• Excessive (toxic) thiamine is hard to achieve unintentionally

Question 3

Vitamin B₂ (Riboflavin) - Energy (Redox/Respiration)

Answer 3

• Main Functions:
  
  • Component of FAD and FMN - Central to cellular respiration
• Dietary necessity for:
  
  • All animals
• Deficiency usualy presents as non-specific symptoms
  
  • mucus membrane inflammation, alopecia, dermatitis, anemia
  • Rarely Fatal
• Excessive (toxic) riboflavin is hard to achieve unintentionally

Question 4

Vitamin B₃ (Niacin) - Energy (Redox/Respiration)

Answer 4

• Main Functions:
  
  • Component of NAD⁺ and NADP⁺ - central to cellular respiation
• Dietary necessity for:
  
  • Niacin can be synthesized in the body from nicotinamide or tryptophan
    
    • Tryptophan often most impotant
  • Sufficient intake of tryptophan/nicotinamide/niacin is required
  • B₆ deficiency or excess leucine can inhibit Tryptophan -> niavin synthesis
• Deficiency usually presents as weakness and loss of appetite and, in severe cases, dermatitis, diarrhea, and dementia (pellagra)
• Excessive (Toxic) niavin is hard to achieve unintentionally (may reduce cholesterol synthsis)

Question 5

Vitamin B₅ (Pantothenic Acid) - Energy (Coenzyme A)

Answer 5

• Main Functions:
  
  • Component of Coenzyme A
  • Component of phosphopantetheine (Acyl carrier protein)
• Dietary necessty for:
  
  • Growing animals (especially chicks)
• Deficiency is rare (secondary to general malnutrition)
• Excessive (toxic) pantothenic acid is hard to achieve unintentionally

Question 6

Vitamin B₆ (Pyridoxine) - Energy (Glycogen)

Answer 6

• Main Functions:
  
  • Binds to hemoglobin (O₂ transport?)
  • Cofactor for hundreds of reactions including gluconeogenesis, glucolysis, AA metabolism, etc.
  • Glycogen phosphorylase accounts fo >70% of B₆
• Dietary necessity for:
  
  • All animals
• Deficiency is rare but may present as hyperirritability, seizures, and oral inflammation
• Excessive pyridoxine may lead to neuropathy and CNS confusion

Question 7

Vitamin B₇ (Biotin) - Energy (Carboxylation)

Answer 7

• Main Functions:
  
  • Carboxylation reactions
    
    • Pyruvate carboxylase, propionyl-CoA carboxylase, Acetyl-CoA carboxylase, B-methylcrotonyl-CoA carboxylase
• Dietary necessity for:
  
  • All animals
• Deficiency is rare and usually caused by deficient utilization, not diet
  
  • Presents as dermatitis, alopecia, weakness
• Excessive (toxic) Biotin is hard to achieve unintentionally

Question 8

Vitamin B₉ (Folic Acid) - Hematopoiesis (methylation)

Answer 8

• Main Functions:
  
  • Biosynthesis of purines/pyrimidines
    
    • needed by rapidly dividing cells
  • Methionine synthesis
    
    • indirectly through cobalamin
  • Neural tube closure (mechanism?)
• Dietary necessity for:
  
  • All animals
• Deficiency usually presents as anemia due to impaired hematopoiesis or abnormal growth in juveniles
  
  • extreme deficiency can lead to death
• Excessive folic acid has not been described
• Sulfa drugs act to inhibit folate synthesis in bacteria

Question 9

Vitamin B₁₂ (Cobalamin) - Hematopoiesis (methylation)

Answer 9

• Main Functions:
  
  • Methionine synthesis
  • Purine/pyrimidine synthesis (indirectly through folate)
  • Conversion of propionate to succinyl-CoA
    
    • gluconeogenesis, synthesis of myelin
• Dietary necessity for:
  
  • Non-ruminants (ruminant microbes synthesize)
• Deficiency is rare, caused by diet or deficiency in absorption, presents as pernicious anemia
  
  • cattle can have deficiency when fed cobalt deficient feed
• Excessive cobalamin has not been described

Question 10

Vitamin C (Ascorbic Acid) - Antioxidant (Redox Reactions)

Answer 10

• Main functions:
  
  • Soluble antioxidant
  • Hydroxylation reactions
    
    • Hydroxyproline/lysine for collagen
    • Hydroxylation of dopamine to norepinephrine
    • Hydroxylation of cholesterol toward bile acids
  • Reduction of Fe³⁺ to Fe²⁺ in intestine for iron absorption
• Dietary necessity for:
  
  • Most animals synthesize from glucose
  • Not primates, fish, songbirds, flying mammals, or guinea pig (dietary)
• Deficiency usually presents as immunosuppression or connective tissue disorders
• Excess vitamin C can lead to kidney stones or iron overload

Question 11

Fat Soluble vitamins

Answer 11

• Vitamin E, Vitamin A, Vitamin D, Vitamin K

Question 12

Vitamin E - Antioxidant

Answer 12

• Main Functions:
  
  • Lipid antioxidant
• Dietary necessity for:
  
  • All animals, amount needed varies partially based on dietary intake of unsaturated fatty acids
  • Packaged in chylomicrons/lipoproteins in blood
• Deficiency presents as erythrocyte fragility, nerve and muscle disorders due to Ca²⁺ influx into cells, may lead to sudden death
• Excess vitamin E is not as toxic as other fat-soluble vitamins, but can have an anti-coagulative effect

Question 13

Vitamin A - Vision (photosensitive)

Answer 13

• Main Functions:
  
  • Vision (rhodopsin)
  • Growth/differentiation factor (similar to steroid hormones)
• Dietary necessity for:
  
  • All animals, bound to Retinol Binding Protein or albumin in blood
• Deficiency usually presents as visual disorder, cornification of mucosal epithelium, or infertility
• Excess vitamin A occurs after retinol binding proteins have been saturated, leads to liver hypertrophy, skin desquamation, and bone demineralixaiton

Question 14

Vitamin D - Calcium/Phosphate Regulation

Answer 14

• Main Functions:
  
  • Calcium, magnesium absorption (intestine, steroid hormone)
  • Activated at the kidney in response to PTH
• Dietary necessity for:
  
  • Carnivores (mammals can synthesize Vitamin D from cholesterol using UV radiation in the skin, but insufficient amounts are produce by carnivores)
  • Bound to Vitamin D binding protein in blood
• Deficiency usually presents as abnormal bone mineralization and hypocalcemia
• Excess Vitamin D causes hypercalcemia/hyperphosphatemia/kidney stones

Question 15

Vitamin K - Coagulation (Koagulation)

Answer 15

• Main Funtions:
  
  • Carboxylation
  • Maturation of clotting factors
  • Bone metabolism
• Dietary necessity for:
  
  • All animals, but easily accessible and ruminants microbes synthesize sufficient amounts for ruminants
  • Packaged in chylomicrons/lipoproteins in blood
• Deficiency presents as clotting disorders, severe deficiency can lead to death
• Excess Vitamin K is rare
  
  • Water Soluble K₃ may cause gastrointestinal disorders and anemia

Question 16

Clotting

Answer 16

Question 17

Vitamin K and Clotting Factors

Answer 17

Question 18

Vitamin K and Warfarin

Answer 18