Fol, B12, SAM Flashcards
What happens at the Pteridine ring of Folate?
Contains the site of oxidation and reduction.
Sulfa drugs are an analog of what structure of Folate?
Para-aminobenzoic acid (PABA)
Most of the Folate in the body is reduced to what form?
FH4 - tetrahydrofolate
Dihydrofolate is oxidized or reduced to Tetrahydrofolate?
Oxidized
Damage to the intestinal mucosa, such as in Crohn’s, Alcoholism, and Celiac disease, can cause an inhibition of absorption of what substance?
Folate
What is the most oxidized form of FH4?
N10-formyl-FH4
What is the most reduced form of FH4?
N5-methyl-FH4
When FH4 is trapped as N5-methyl-FH4 and cannot be oxidized, it can cause what type of deficiency?
Functional folate deficiency
What is the major source of carbon for the one carbon pool?
Serine, from dietary carbs as 3-phosphoglycerate
FH4 is needed for what type of base synthesis?
Purine synthesis (ultimately DNA synthesis)
The cancer drug 5-fluorouracil targets this reaction.
The production of dTMP from dUMP via N5N10-methylene-FH4
The cancer drug Methotrexate targets what reaction?
The rxn of dihydrofolate reductase
Converts FH2 to FH4
B12 has two forms in the body, what are they?
Methylcobalamin and 5’-deoxyadenosylcobalamin
Vitmain B12 contains what metal?
Cobalt
Homocysteine is converted to what, via B12 and Folate?
Methionine
The conversion of Methylmalonyl-CoA to Succinyl-CoA requires what?
Vitamin B12
Vegans may develop a B12 deficiency many years after starting their diet. Why is this?
B12 is absorbed in the liver and stored there in excess.
Pernicious Anemia is caused by a deficiency in what?
Intrinsic Factor
This substance is secreted by gastric parietal cells, binds to B12 for transport in the intestinal tract, and complexes with transcobalamin II before entering circulation
Intrinsic Factor
During a Schilling test, this substance is labeled in measured in different stages to determine a deficiency in what other substance?
Cobalt is labeled to test for B12 deficiency.
The conversion of Homocysteine to Methionine requires what?
B12 (and folate)
Folate adds one carbon groups to what type of atoms?
carbon or sulfur atoms
SAM adds methyl groups to what type of atoms?
nitrogen or oxygen atoms
SAM is made from what 2 substances?
Methionine and ATP
SAM is a precursor to what substance?
Homocysteine
B12 is trapped in the methylated form when deficient in what?
Homocysteine
This process occurs in the liver and is an alternative pathway for the conversion of Homocysteine to Methionine
Choline –> Betaine, which methylates the sulfur atom of homocysteine
Folate deficiency in pregnant women will eventually show an elevation in what?
Homocysteine
This folate deficiency is caused by decreased synthesis in Thymine and Purine bases. This shows large RBC’s that do not function properly.
Megaloblastic Anemia
An alcoholic can suffer from Megaloblastic anemia due to Folate or B12. Name a test which can differentiate between the two deficiencies.
Measure:
Homocysteine for Folate/B12 deficiency
Methylmalonyl-CoA for B12 deficiency **only one definitive for B12 and rules out Folate
Schilling test shows that a patient is unable to absorb crystalline B12, what is the deficiency?
Low activity of pepsin, which causes the B12 to remain bound to R-binders and not intrinsic factor
