USMLE

Vitamin B7 (Biotin)

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Vitamins
  1. Vitamin B1 (Thiamine) Biochemistry
  2. Vitamin B1 (Thiamine) Deficiency
  3. Vitamin B2 (Riboflavin)
  4. Vitamin B3 (Niacin) Biochemistry
  5. Vitamin B3 (Niacin) Deficiency and Excess
  6. Hartnup Disease
  7. Vitamin B5 (Pantothenic Acid)
  8. Vitamin B6 (Pyridoxine)
  9. Vitamin B7 (Biotin)
  10. Vitamin B9 (Folate)
  11. Vitamin B12 (Cobalamin) Biochemistry
  12. Vitamins B9 and B12 Deficiencies
  13. Vitamin A (Retinol) Biochemistry
  14. Vitamin A (Retinol) Deficiency and Excess
  15. Vitamin C (Ascorbic Acid) Biochemistry
  16. Vitamin C (Ascorbic Acid) Deficiency and Excess
  17. Vitamin D Biochemistry
  18. Vitamin D Deficiency and Excess
  19. Vitamin E (Tocopherol/Tocotrienol)
  20. Vitamin K Biochemistry
  21. Vitamin K Deficiency
  22. Zinc
  23. Kwashiorkor and Marasmus

Summary

Vitamin B7 (Biotin) is a water-soluble vitamin, important in metabolism as a cofactor for several important carboxylase enzymes. Enzymes dependent on biotin include pyruvate carboxylase, acetyl-CoA carboxylase, and propionyl-CoA carboxylase.

Biotin deficiency is rare, but it can be induced by antibiotic usage or excessive consumption of raw egg whites. In particular, the avidin in egg whites binds and sequesters biotin. Patients with a biotin deficiency typically present with dermatitis, diarrhea, and alopecia.

Key Points

  • Biotin (Vitamin B7)
    • cofactor for carboxylation enzymes (adds 1 carbon group):
      • Pyruvate carboxylase (in Pyruvate Metabolism)
        • Pyruvate (3C) → oxaloacetate (4C)
          • first committed step of gluconeogenesis
      • Acetyl-CoA carboxylase (in Fatty Acid Synthesis)
        • Acetyl-CoA (2C) → Malonyl CoA (3C)
      • Propionyl-CoA carboxylase (in Propionic Acid Pathway)
        • Propionyl-CoA (3C) → methylmalonyl-CoA (4C)
          • Important in metabolism of isoleucine, valine, threonine, methionine, and odd-chain FAs
  • Biotin (Vitamin B7) Deficiency
    • relatively rare, seen with:
      • excessive consumption of raw egg whites
        • avidin in egg whites binds biotin, impairing GI absorption
      • broad-spectrum antibiotic use
        • kills biotin-producing bacteria in GI tract
    • symptoms include dermatitis, enteritis, and alopecia



Find Vitamin B7 and other Vitamins among Pixorize's visual mnemonics for the USMLE Step 1 and NBME shelf exams.