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32 Cards in this Set
- Front
- Back
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what do folate, vit b12, and SAM all have in common?
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all play critical role in metabolism of 1 C units
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sources of 1 C units for tetrahydrofolate
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serine, glycine, histidine, formaldehyde, formate
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products after receiving C from tetrahydrofolate?
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dTMP, serine, purine, vit B12-CH3
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3 major parts of folate?
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pteridene ring, PABA, glutamate tail
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how to convert to active form of folate?
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2 reduction rxns to convert to FH4
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what is the major form of folate in blood? (most reduced?)
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N5 methyl FH4
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what is methotrexate
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inhibits dihydrofolate reductase, FH2 to FH4, cancer therapy drug. Like folic acid, comp inhibitor
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imp of vit B12 structure?
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corrin ring-Cobalt-form C bonds, cleaved to form free radical rxns
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what 2 rxns are B12 involved in?
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methylmalonyl to succinyl CoA, homocystein+methyl to methionine
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when does methylmalonyl CoA to succinyl CoA occur?
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1. oxid of odd chain FA 2. degradation of branched aa
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SAM stands for?
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S-adenosylmethionine
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what is SAM synthesized from?
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methionine + ATP
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what are some rxns SAM is involved in?
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NE to EPI, forms creatine, methylated nucleiotides, phosphatidylcholine, melatonin
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more than 35 rxns require what from SAM? Where on structure?
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methyl donation, added to N
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after methyl donated, SAM is converted to
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homocysteine, cleaves branch wihtout methyl
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homocysteine is converted to via methyl group from B12
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methionine to eventually form SAM
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where does Vit B12 get the extra methyl group to give to homocysteine to form methionine?
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FH4-CH3( N5 methyl FH4)
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point of relationship between FH4, B12 and SAM?
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total objective is to generate SAM, relate it to glucose
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where can you get B12?
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meat, anaerobic bacteria
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where is B12 stored?
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liver
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absorption and transport of vit B12? Fcn of intrinsic factors?
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binders in stomach, pancreas digest binders, intrinsic factors from stomach bind to B12, transport to receptors in ileum-absorbed to blood
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what happens when there is a B12 deficiency? What builds up
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homocysteine, methylmalonyl CoA, N5 Methyl FH4
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significance of N5 methyl FH4 rxn?
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irreversible--leads to def in folate, leads to megaloblastic anemia
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why is it important to find cause of megaloblastic anemia?
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if just give folate, can mask B12 deficiency, lead to neurological damage
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usual defect of B12 deficiecny? Trtmnt?
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uptake, not diet. Injection treatment
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what defect is correlated to folic acid deficiency?
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neural tube defect--anencephaly, spina bifida
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what is hyperhomocysteinemia?
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increased homocysteine, treated with folic acid, folic acid and B12 defic
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what feedback inhibition on what enzyme occurs when increased homocysteine and leads to increased cysteine?
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inhibition on cystathionine B synthase
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what 2 ways can homocysteine be converted to methionine?
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B12, betaine to make dimethyl glycine
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2 causes of folic acid deficency to cancer?
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overwhelms U-repair system in DNA replication, repair can generate double strand break
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pros of dietary folic acid supplementation?
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reduces neural tube defect, reduces homocysteine levels, may reduce some cancer risk
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cons of dietary folic acid supplementation?
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may suppress evidence of B12 deficiency, appears to promote growth of cancerous cells(increase rate), increase synthetic folic acid(not natural)
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