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Flashcards in Folic Acid and B12 Deck (21)
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name the one carbon donors in metabolism

  • SAM
  • THF
    • one carbon groups are derived from catabolism of amino acids (gly, ser, his, trp)
  • cobalamin


describe S-adenosyl methionine (SAM)

  • synthesized from methionine
  • methyl group donor in:
    • synthesis of epinephrine
    • synthesis of creatine
    • formation of phoshpholipids 
  • after donating its methyl group, SAM is coverted to homocysteine
    • can be converted to cysteine through the transulfuration pathway (requires PLP)
    • conversion back to methionine (requires B12 and methylfolate)


SAM is synthesized from _____

SAM is synthesized from methionine


SAM Is a methyl group donor in.... (3 rxns)

SAM Is a methyl group donor in:

  1. synthesis of epinephrine
  2. synthesis of creatine
  3. synthesis of nucleotide bases
  4. formation of phospholipids (phosphatidylcholine)



after donating its methyl group, SAM is converted to ____ which can have 2 fates--explain

after donating its methyl group, SAM is converted to homocysteine which can have 2 fates

  1. conversion to cysteine through transulfaration pathway (requires PLP)
  2. conversion back to methionine (requires B12 and methylfolate)


describe the fate of homocysteine pathway


deficiency of which 3 vitamins would lead to increased homocysteine levels?

  • folate
  • B12
  • B6


describe THF synthesis and the 1 reaction it is important for

  • THF is formed from dietary folic acid
  • THF is formed from folate by dihydrofolate reductase
  • Methyl-THF is of primary importance for formation of methionine from homocysteine



describe the formation of THF pathway (and drugs)


describe the forms of THF in the 1-C pool

  • formyl THF and methylene THF are used as 1-C donors for synthesis of purine and pyrimidines (thymidine)
  • methyl THF is used ONLY in the conversion of homocysteine to methionine (the rxn also requires B12)
    • methyl THF might be considered as the "storage" form of THF


describe the pathway for different forms of THF 


describe what changes occur in folate deficiency

  • reduction in 1-C donors, resulting in reduced synthesis of purine and pyrimidine nucleotides
  • delay in DNA synthesis resulting in reduces rates of cell division
  • effects on RBC formation
  • decrease in hemoglobin concentration
    • macrocytic, megaloblastic anemia
  • polysegmented neutrophils in blood smear


describe how folate deficiency can be detected/tested


describe vit. B12 deficiency

  • deficiency of vit. B12 is characterized by macrocytic anemia and neurological features (tingling sensaiton in hands and feet, urinary incontinence)
  • vit. B12 is absorbed in terminal ileum as a complex of B12 and the intrinsic factor
  • intrinsic factor is released from parietal cells of stomach


which 2 rxns require B12 as a coenzyme?

  • methionine synthase
  • methylmalonyl CoA mutase



which levels are elevated in vit. B12 deficiency?

  • increased levels of methylmalonate
  • elevated homocysteine levels
  • patients with vit. B12 deficiency also have deficiency of the usable form of folate; this is Folate trap


describe the mechanism of folate trap


describe a summary of folate and B12 deficiency pathway


contrast folate and B12 deficiency