Vitamin B12 and Folic Acid Flashcards
–Specify the one-carbon donors in metabolism and the groups they donate (SAM, THF, Cobalamin) –Explain the formation of SAM and the reactions requiring SAM –Analyze the metabolism of homocysteine, vitamins/ coenzymes required for metabolism & interpret the clinical significance of homocysteine –Explain the formation of THF from folate and specify the mechanism of action of their inhibitors –Summarize the formation of one carbon groups from amino acid metabolism and the utilization of 1-C gro
What is another name for Vitamin B12?
Cobalamin
What are sources for Vitamin B12?
Meats
Shellfish
Poultry
Eggs
Diary products
(not present in plants)
What are the active forms of Vitamin B12?
5-deoxyadenosylcobalamin
methyl cobalamin
How does SAM act upon substrates?
methylation of substrates
How is SAM formed?
Made from adenosine triphosphate (ATP) and methionine by methionine adenosyltransferase.
What are the two major disposal pathways for homoscysteine?
-Conversion to methionine (Req: Folate & B12) - remethylation
-Conversion to Cysteine (Req: B6/Pyridoxine) - transsulfuration
Deficiency of B12 results in the accumulation of Homocysteine and the…
trapping of THF in the methyl-THF form
The trapping of THF in the methyl-THF form due to B12 deficiency impairs synthesis of what?
Nucleotide synthesis
DNA and RNA synthesis
trapped form of THF is known as
N5-methyl H4folate
THF is short for?
Tetrahydrofolate
Homocysteine + N5-Methyltetrahydrofolate undergo catalysis by which enzyme to form what?
Enzyme: Methionine synthase
Product: L-Methionine + THF
Oxidation of odd-chain fatty acids generate which three carbon fatty acid by-product?
Propionyl-CoA
Propionyl CoA carboxylase requires what?
Biotin
What is another name for methionine synthase?
Homocysteine N-Methyltransferase
Pernicious anemia associated with homocystinuria specifically results from?
No intrinsic factor because of autoimmune destruction of parietal cells (therefore can’t absorb B12)