The One Carbon Pool Flashcards
True or False: In a one-carbon carrier the carbon can be in a number of oxidation states.
TRUE
What are groups containing a one carbon fragment that can be transferred from one compound to another?
A one-carbon pool
What is a one-carbon carrier of carbon dioxide?
Biotin
Derivatives of of what, carry one-carbon units in all oxidation states except carbon dioxide?
Tetrahydrofolate (THF)
What is the principal donor of active methyl groups?
S-adenosylmethionine (SAM)
Folate is a vitamin because humans cannot synthesize what?
Pterin ring
Prior to absorption dietary folate (folic acid) must be what? (2)
Deconjugated and reduced
Processing of folate is carried out by a reductase and a conjugase where?
In the brush border of the intestinal epithelial cells
A cellular conjugase adds what to folate within cells?
Glutamate residues
True or False: in metabolism of folate, one carbon units cannot be interconverted.
False (they can)
True or False: 5-methyltetrahydrofolate cannot be oxidized.
True (it cannot be oxidized)
What is the major amino acid source of one-carbon groups among folate derivatives?
Serine
Glycine, histidine, and formate are additional (serine being the primary one) sources of what among AA derivatives of folate?
One-carbon groups
What is used to generate SAM?
Methyl cycle
What is the immediate precursor of SAM?
Methionine
What is produced from hydrolysis of SAM?
Homocysteine
What enzyme regenerates methionine from homocystein?
Homocysteine methyltransferase
Activated methyl from N5 - methyltetrahydrofolate and vitamin B12 (methylcobalamin) are cofactors for what reaction?
Regeneration of methionine from homocysteine
Converting homocysteine to cysteine can be done in two steps. What is the intermediate product?
Cystathionine
What is the cofactor in both of the two steps required to convert homocysteine to cysteine?
Pyridoxal phosphate
What hypothesis explains why some macrocytic anemias respond to B12 or folate treatments?
The methyl trap hypothesis
Valine, methionine, isoleucine, and threonine can be degraded to what?
Succinyl CoA
Conversion of propionyl CoA requires what?
Biotin
What is a common intermediate in the catabolism of valine, methionine, isoleucine and threonine?
Methylmalonyl CoA
What is the cofactor for methylmalonyl CoA mutase?
B12
What results from a defect in methylmalonyl CoA mutase?
Methylmalonic aciduria
True or False: some forms of methylmalonyl aciduria respond to high doses of vitamin B6.
False (it’s B12)
What does dietary B12 bind to?
R-binders in the stomach
What destroys R-binders?
Pancreatic proteases
What does free B12 bind to?
Intrinsic factor (IF)
Where is B12-IF complex absorbed?
Ileum
B12 cirbulates as what?
A transcobalamin complex
Where is B12 stored?
Liver
