B12 Folate Metabolism & Absorption Flashcards
Retarded synthesis of DNA due to B12 deficiency results in what?
Megaloblastic macrocytic anemia
What are the characteristics of megaloblastic macrocytic anemia?
Large erythroid precursors, ↓ mitotic divisions, delayed nucelar development, ↑ cytoplasmic volume
What is the clinical presentation of megaloblastic macrocytic anemia?
MCV >100
Lethargy, weakness, yellow or waxy pallor, loss of weight & appetite, diarrhea
Blood smear: many enlarged oval macrocytes
Bone marrow: large erythroblasts (megaloblasts), neutrophils w/ >5 lobes
What are neurological symptoms of megaloblastic macrocytic anemia?
peripheral neuropathy (pins & needles, ↓ambulation, ↓memeory), “megaloblastic madness”
What is the dietary form of folate?
Dihydrofolate (DHF)
What is the active form of folate?
Tetrahydrofolate (THF)
What reduces DHF to THF?
Dihyrofolate reductase, adds 2* H⁺
What is the function of THF?
Transfer carbon units (CH₃) from donors to acceptors
Detail the folic acid pathway?
DHF + DHF reductase→ THF→ + N⁵,¹⁰-mehylene THF→ dUMP + C→ DHF & dTMP→ DNA
When does the main carbon transfer of folate metabolism?
Transfer of the carbon side chain of serine to N⁵,¹⁰-mehylene THF
Sources of DHF?
Most foods including eggs, milk, yeast & especially abundant in leafy vegetables
What are causes of folate deficiency?
Inadequate dietary intake (most common), malabsorption, pregnancy, drugs
Who are most likely to suffer from folic acid deficiency?
Poor & elderly, alcoholics
What are the folic acid requirements & how is it stored?
50 ug needed/day, 50-80% of ingested is absorbed in small intestine.
Liver stores 5-10 mg that can last 3-6 mths
What form of folate is found in circulation?
N⁵-mehyl-THF
