SYLLABUS 17: Metabolism of 1C Fragments, Folic Acid Biochemistry Flashcards Preview

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Flashcards in SYLLABUS 17: Metabolism of 1C Fragments, Folic Acid Biochemistry Deck (27):

what is the active form of folic acid? how's it formed?

folic acid is derived from the diet or ingested as a vitamin 

it's reduced by dihydrofolate reducates to dihydrofolate, DHF or FH2 

DHF is reduced by dihydrofolate reducatase to tetrahydrofolate, THF or FH4 

THF or FH4 is the active cofactor form 

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how does THF function

it transfers single carbon atoms in several critical biochemical reactions 


what are the carbon atoms THF uses in biochemical reactions?

which is most reduced/oxidized?

1) methyl group -CH3: the most reduced C

2) methylene group -CH2: intermediately reduced C 

3) methenyl group =CH: most oxidized C

4) formyl group -HC=O which is equivalent to methenyl 

5) formimino group HC=NH which is equivalent to methenyl


how to carbons attach to THF?

to nitrogen 5 or nitrogen 10 or both nitrogens 5 and 10

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what is the structure of the most reduced form of C that THF can carry



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what is intermediately reduced form of C that THF can carry 

N5, N10-methylene-tetrahydrofolate


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what is most oxidized form of C that THF can carry?

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what is the fate of the intermediate N5,N10 methylene THF?

1) can be used directly

2) can be reduced to the N5CH3 THF by methylene THF reductase 

3) can be oxidized to N5-HC=N10 methenyl THF 



what is the fate of the N5-CH=N10 methenyl THF?

1) it can be used directly 

2) it can be reduced to the N5-CH2-N10 methylene THF 



what are the major donors of C atoms to the folic acid pool?

amino acids: serine, glycine, histidine 


what do serine and glycine do re: THF production

each donates a carbon atom to produce N5-CH2-N10 THF, methylene THF 

this product can be used or reduced or oxidized


what does histidine do re: THF production 

breaks down to produce N-formiminoglutamic acid, which reacts w/ THF to form glutamic acid + N5-formimino THF 

this is equivalent to methenyl THF 

this product can be used or reduced 


what is the relationship between serine and glycine re: THF

glycine serine 



how many serines are neede dto produce 2 N5-CH2-N10 THF

1 serine


what biochemical reaction is N5CH3THF used in

aka methyl B12

it regenerates methionine from homocysteine 

thus when we regenerate methionine, the methyl group could've come from serine, glycine, or histidine 


what biochemical reaction is N5-HC=N10 methenyl THF used in 

provides 2 of the C atoms in the synthesis of purine rings


what biochemical rxn is N5-CH2-N10 methylene THF used for? 

synthesize dTMP from dUMP 

this is part of pyrimidine synthesis pathway 

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how does 1 C unit get transferred from N5, N10 methylene FH4 to dUMP to form dTMP?

1. thymidylate synthase uses N5, N10 methylene FH4 and produces deoxythymidine monophsphate, dTMP 

this produces FH2, dihydrofolate (DHF) 

2. dihydrofolate reductase uses NADPH to reduce DHF back to THF 

3. THF picks up a C from serine and restarts the cycle 

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which is the active form - THF or DHF?



what cancer drugs inhibit the dUMP -> dTMP reaction? 

how do they work? 

1. 5-Fluorouracil inhibits thymidilate synthase which produces dTMP from dUMP 

2. Methotrexate (aka aminopterin, amethopterin) inhibits dihydrofolate reductase which regenerates DHF from THF; this inhibits thymidine synthesis and purine synthesis, and works as an anti-inflammatory


what can you do for a patient you suspect has a folate deficiency?

give them an injection of histidine

assay for formamino glutamic acid in their blood 


what is pernicious anemia? 

what causes it? 

when there's a deficiency in glycoprotein, intrinsic factor, which is needed for absorption of B12 

this causes disturbances of folate metabolism as N5-CH3-THF accumulates cannot go back to N5-methyl-N10-THF, as this reaction requires B12 

no IF = no B12 = folate metabolism is messed up, and most of C atoms in Folate pool accumulate as N5-CH3-THF 

this means you run out of N5-N10-methylene-FH3 and cannot synthesize C atoms 2 and 8 of the purine ring


what is most reduced form of carbon carried in fotale pool? 

most oxidized form? 

most reduced: methyl, CH3 

most oxidized: methenyl; equivalent to formyl, forminino


serine can eventually donate 2 of its C atoms to folate pool 


is glycine an essential aa? 

Serine eventually donates 2 of its C atoms to the folate pool by adding C to THF to
regenerate N5, N10-Methylene FH4.

Glycine is a non-essential amino acid because it can
be produced from serine by loss of a C. 


each form of C carried in folate pool can participate in produciton of an important biochemical. name the reacitons 

methyl carbon: regenerates methionine from homocysteine

methylene carbon: used to syntheisze dTMP from DUMP 

methenyl carbon: used to provide 2 of the C atoms in purine ring synthesis


why are methotrexate and 5-fluorouracil used as anti-cancer drugs? 

Methotrexate is anti-tumor drug because it inhibits the dihydrofolate reductase
reaction, which takes DHF -> THF using NADPH, making THF active and allowing for
resynthesis of N5, N10-methylene FH4, which is important for making new dTMP from
dUMP, or DNA/RNA synthesis. Blocking this means blocking new nucleic acid synthesis.
5-fluorouracial is an anti-tumor drug because it blocks the thymidilate synthase
reaction, which synthesizes dTMP from dUMP. 


why does folat edeficiency result in anemia and growth failure? 

Folate deficiency results in growth failure because folate metabolism is integral to the
synthesis of dUMP to dTMP which is important for growth and development. It also
causes pernicious anemia because when there’s a deficiency in Intrinsic Factor or
Glycoprotein, there are disturbances to folate metabolism since the methyl-THF
accumulates and cannot go back to the N5-methyl-N10-THF because this reaction
requires B12. No B12 means that most of the C atoms in the Folate pool accumulate as
N5-methyl-THF so you run out of N5-N10-methylene-FH3 and cannot synthesize C
atoms 2 and 8 of the purine ring. 

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