Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
12 Cards in this Set
- Front
- Back
|
blank
|
blank
|
|
|
Specify the one-carbon donors in metabolism and the groups they donate (SAM, THF, cobalamin)
|
Donors - Serine, glycine, histidine, formate and formaldehyde
CO2 is NOT a 1-carbon donor Donated groups - methyl, formaldehyde, formic acid or carbonic acid. Carriers - Tetrahydrofolate (THF) - primary Methylcobalamin - based on vitamin B12 S-adenosylmethionine (SAM) - methylation reactions |
|
|
Explain the formation of SAM and the reactions requiring SAM
|
Formation - ?
Reactions requiring SAM - methylation reactions Norepenephrine → Epinephrine Guanidoacetate → Creatine Phosphotidylethanolamine → Phosphatidylcholine Acetylserotinin → Melantonin Nucleotides (DNA) → Methylated Nucleotides |
|
|
Analyze the metabolism of monocysteine, vitamins/coenzymes required for metablism and interpret the clinical significance of homocysteine
|
Monocysteine metabolism ?
Vit required ? Homocysteine - ? |
|
|
Explain the formation of THF from folate and specify the mechanism of action of their inhibitors
|
Folate (inactive form) is reduced to Dihydrofolate and then reduced again to Tetrahydrofolate (active form).
Method of inhibition ? |
|
|
Summarize the formation of one carbon group from amino acid metabolism and the utilization of 1-C groups for nucleotide synthesis
|
?
|
|
|
Indicate the different forms of THF (formyl, methylene and methyl) and reactions requiring the different forms of THF
|
A 1-carbon group can be carried and donated either as formyl (-CH=O), methylene (-CH2-) or methyl (-CH3)
Formyl THF and methylene THF are used as 1-C donors for synthesis of Purines & Pyrimidines Methyl THF is only used in the converstion of Homocysteine to Methionine Methyl THF is considered the storage form. |
|
|
Identify the reactions requiring B12
|
1. Methylmalonyl CoA rearrangement to Succinyl CoA - needed to remove 3C products of fatty acid and amino acid metabolism by facilitating their transfer to TCA cyce
2. Remethylation of Homocysteine to Methionine - Sole method to release THF from methyl-THF. Stops Methyl-Trap |
|
|
Compare and contrast the causes of folate and vitamin B12 deficiency
|
Folate defciency - caused by dietary lack, impaired absorption (intestine), increased requirement (pregnancy), antagonists (anti-cancer drugs)
Vitamin B12 deficiency - dietary lack, lack of IF, gastrectomy, increased demand (pregnancy) |
|
|
Indicate the role of intrinsic factor in vitamin B12 absorption
|
1. B12 binds to IF in the duodenum
2. Transport to the ileum. 3. B12 associates with a carrier protein (Transcobalamin II) 4. Delivery to the liver. |
|
|
Justify the mechanism of the occurrence of folate trap in B12 deficiency
|
If vitamin B12 is deficient, Tetrahydrofolate which has been methylated is trapped in that form as methionine synthase (homocysteine methyltransferase) is B12 dependent.
|
|
|
Compare and contrast the clinical and biochemical features of folate and vitamin B12 deficiency
|
Tetrahydrofolate (active form) requires Vit B12 (methy-cobalamin) to form during the methyl transfer to homocysteine in the creation of Methionine. It is derived from N5-methyl-tetrahydrofolate. Lack of B12 locks THF into methyl-THF
Lack of Tetrahydrofolate can be due to either a lack of folic acid OR vitamin B12. Folic acid and cobalamin are both prescribed in megaloblastic anemia. |
