Term
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Definition
| Tyrosine --> DOPA (Tyr Hydrolase, BH4) |
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Term
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Definition
| Tyrosine --> DOPA (Tyr Hydrolase, BH4; Rate-limiting step) à Dopamine (Decarboxylase, PLP (B6)) |
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Term
| How is Norepinephrine made? |
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Definition
| Tyrosine --> DOPA (Tyr Hydrolase, BH4; Rate-limiting step) --> Dopamine (Decarboxylase, PLP (B6)) --> Norepinephrine (Hydroxylase containing Vit. C and Cu) |
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Term
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Definition
| Tyrosine --> DOPA (Tyr Hydrolase, BH4; Rate-limiting step) --> Dopamine (Decarboxylase, PLP (B6)) --> Norepinephrine (Hydroxylase containing Vit. C and Cu) --> Epinephrine (N-Methyltransferase, SAM as methyl donor) |
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Term
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Definition
| Tyrosine --> Melanins (Deficiency = albinism) |
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Term
| What neurotransmitters does Tryptophan produce? |
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Definition
| Serotonin and melatonin. (Also NAD+ and Niacin.) |
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Term
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Definition
| Glutamate --> Gamma-Aminobutyric Acid + CO2 (Glutamate decarboxylase, PLP) |
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Term
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Definition
| Histidine --> Histamine + CO2 (Histadine decarboxylase, PLP?) |
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Term
| What are one-carbon groups needed for? |
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Definition
| Formation of Methionine, Biosythesis of purines/pyrimidines, Biosynthesis of Glycine from CO2 and NH4+ by Glycine synthase |
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Term
| Name the major one-carbon group carriers. |
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Definition
| Biotin (CO2), THF (All oxidation states except CO2), SAM (CH3), Vitamin B12/Cobalamin (CH3) |
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Term
| How do humans sythesize the pterin ring in BH4? |
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Definition
| They don't. Folate is needed from the diet. Polygultamines are cleaved by conjugase in intestinal mucosal cells giving rise to folate. Folate is reduced to DHF and then again to THF using Dihydrofolic Acid Reductase (NADPH2). |
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Term
| How can THF carry so many different "forms" carbon? |
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Definition
| Carbon fragments can bond to either or both of the 5 or 10 position nitrogens in different oxidation states. -CH3 (5=methyl); -CH2- (5,10=methylene); -CHO (5=formyl); -CHNH (5=formino); -CH= (5,10=methenyl). These can interconvert. |
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Term
| What AA conversion uses THF? |
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Definition
| Serine + THF --> Glycine + 5,10-methylene-THF. |
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Term
| What are some deficiencies and therapeutic uses associated with folate? |
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Definition
| If folate is deficient during pregnancy, spinal tube defects can result. Folate deficiency can also arise from oral contraceptives and barbiturates. Chemotherapy med's like methotrexate also create deficiency so that rapidly dividing cells (tumors) can't synthesize pyrimidines. |
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Term
| What AA makes a good donor of methyl groups? |
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Definition
| Methionine. Since it has a sulfur separating -CH3 from the rest of the R-group, it can bind to adenosyl from ATP to create S-Adenosylmethionine (SAM). |
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Term
| What reactions does SAM play a part in? |
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Definition
| 1) Norepi --> Epi, 2) Guanidinoacetate --> Creatine, 3) Acetyeserotonin --> Melatonin, 4) Phosphatidylethanolamine --> Phosphtatidylcholine, 5) Methylation of DNA |
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Term
| What products are SAM hydrolyzed to? |
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Definition
| Adenosine and homocysteine. Methionine can be regenerated from homocysteine using 5-methyl THF and the methylcobalamin form of B12. Homocysteine can also yield cysteine (one less C in R group) through PLP. Buildup of Homocysteine (homocysteinuria) is common and usually due to deficiency in methylene-THF reductase. |
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Term
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Definition
| Deficiency in cystathionase which catalyzes Cystathionine --> A-KButyrate. |
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Term
| If Methionine can be made from homocysteine, then why is it essential? |
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Definition
| You need a way to make homocysteine! Homocysteine --> Cysteine is non-reversible. Note that Homocysteine à Methionine is catalyzed by Homocysteine methyltransferase (B12/cobalamin), which is the only enzyme to use N5-methyl form of THF. |
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Term
| Trace the voyage of C from glycolysis to SAM. |
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Definition
| Glycolysis à Serine --> Glycine 5,10-methylene THF --> 5-methyl THF --> B12/cobalamin --> Homocysteinemethyltransferase à SAM |
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Term
| What two RXN's in the body use B12/cobalamin? |
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Definition
| 1) Homocysteine --> Methionine (Homocysteinemethyl transferase) 2) Methylmalonyl CoA --> Succinyl CoA |
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Term
| What is the cause and result of B12 deficiency? |
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Definition
| Problem with intrinsic factor, which carries B12 from gut to bloodstream. Elderly and people with GI tract removal show this. B12 deficiency results in demyelination and spinal cord degeneration since there is 1) a problem in methylmalonyl CoA conversion to Succinyl CoA and 2) excess folate in the diet (folate trap=folate trapped in 5-methyl form). |
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