Page 112 - First Aid for the USMLE Step 1 2020, Thirtieth edition [MedicalBooksVN.com]_Neat
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68 SECTION II BIOCHEmISTRY ``BIOCHEMISTRY—NUTRITION BIOCHEmISTRY ``BIOCHEMISTRY—NUTRITION
Also called biotin.
Vitamin B 7
FUNCTION Cofactor for carboxylation enzymes (which add
a 1-carbon group):
Pyruvate carboxylase: pyruvate (3C)
oxaloacetate (4C)
Acetyl-CoA carboxylase: acetyl-CoA (2C)
malonyl-CoA (3C)
Propionyl-CoA carboxylase: propionyl-CoA
(3C) methylmalonyl-CoA (4C)
DEFICIENCY Relatively rare. Dermatitis, enteritis, alopecia. “Avidin in egg whites avidly binds biotin.”
Caused by long-term antibiotic use or
excessive ingestion of raw egg whites.
Vitamin B 9 Also called folate.
FUNCTION Converted to tetrahydrofolic acid (THF), a Found in leafy green vegetables. Absorbed in
coenzyme for 1-carbon transfer/methylation jejunum. Folate from foliage.
reactions. Small reserve pool stored primarily in the liver.
Important for the synthesis of nitrogenous bases
in DNA and RNA.
DEFICIENCY Macrocytic, megaloblastic anemia; Deficiency can be caused by several drugs (eg,
hypersegmented polymorphonuclear cells phenytoin, sulfonamides, methotrexate).
(PMNs); glossitis; no neurologic symptoms (as Supplemental maternal folic acid at least 1 month
opposed to vitamin B 12 deficiency). prior to conception and during early pregnancy
Labs: homocysteine, normal methylmalonic to risk of neural tube defects. Give vitamin B 9
acid levels. Seen in alcoholism and pregnancy. for the 9 months of pregnancy.
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