Folic Acid and B12

Question 1

name the one carbon donors in metabolism

Answer 1

• SAM
• THF
  
  • one carbon groups are derived from catabolism of amino acids (gly, ser, his, trp)
• cobalamin

Question 2

describe S-adenosyl methionine (SAM)

Answer 2

• synthesized from methionine
• methyl group donor in:
  
  • synthesis of epinephrine
  • synthesis of creatine
  • formation of phoshpholipids
• after donating its methyl group, SAM is coverted to homocysteine
  
  • can be converted to cysteine through the transulfuration pathway (requires PLP)
  • conversion back to methionine (requires B12 and methylfolate)

Question 3

SAM is synthesized from _____

Answer 3

SAM is synthesized from methionine

Question 4

SAM Is a methyl group donor in…. (3 rxns)

Answer 4

SAM Is a methyl group donor in:

1. synthesis of epinephrine
2. synthesis of creatine
3. synthesis of nucleotide bases
4. formation of phospholipids (phosphatidylcholine)

Question 5

after donating its methyl group, SAM is converted to ____ which can have 2 fates–explain

Answer 5

after donating its methyl group, SAM is converted to homocysteine which can have 2 fates

1. conversion to cysteine through transulfaration pathway (requires PLP)
2. conversion back to methionine (requires B12 and methylfolate)

Question 6

describe the fate of homocysteine pathway

Answer 6

Question 7

deficiency of which 3 vitamins would lead to increased homocysteine levels?

Answer 7

• folate
• B12
• B6

Question 8

describe THF synthesis and the 1 reaction it is important for

Answer 8

• THF is formed from dietary folic acid
• THF is formed from folate by dihydrofolate reductase
• Methyl-THF is of primary importance for formation of methionine from homocysteine

Question 10

describe the formation of THF pathway (and drugs)

Answer 10

Question 11

describe the forms of THF in the 1-C pool

Answer 11

• formyl THF and methylene THF are used as 1-C donors for synthesis of purine and pyrimidines (thymidine)
• methyl THF is used ONLY in the conversion of homocysteine to methionine (the rxn also requires B12)
  
  • methyl THF might be considered as the “storage” form of THF

Question 12

describe the pathway for different forms of THF

Answer 12

Question 13

describe what changes occur in folate deficiency

Answer 13

• reduction in 1-C donors, resulting in reduced synthesis of purine and pyrimidine nucleotides
• delay in DNA synthesis resulting in reduces rates of cell division
• effects on RBC formation
• decrease in hemoglobin concentration
  
  • macrocytic, megaloblastic anemia
• polysegmented neutrophils in blood smear

Question 14

describe how folate deficiency can be detected/tested

Answer 14

Question 15

describe vit. B12 deficiency

Answer 15

• deficiency of vit. B12 is characterized by macrocytic anemia and neurological features (tingling sensaiton in hands and feet, urinary incontinence)
• vit. B12 is absorbed in terminal ileum as a complex of B12 and the intrinsic factor
• intrinsic factor is released from parietal cells of stomach

Question 16

which 2 rxns require B12 as a coenzyme?

Answer 16

• methionine synthase
• methylmalonyl CoA mutase

Question 18

which levels are elevated in vit. B12 deficiency?

Answer 18

• increased levels of methylmalonate
• elevated homocysteine levels
• patients with vit. B12 deficiency also have deficiency of the usable form of folate; this is Folate trap

Question 19

describe the mechanism of folate trap

Answer 19

Question 20

describe a summary of folate and B12 deficiency pathway

Answer 20

Question 21

contrast folate and B12 deficiency

Answer 21