Vitamin B12 and Folic Acid

Question 1

Another name for vitamin B12

Answer 1

cobalamin

Question 2

what does the structure of B12 contain

Answer 2

Co and corrin ring system

Question 3

sources of B12

Answer 3

meats, shellfish, poultry, eggs, diary products, NOT IN PLANTS

Question 4

active forms of cobalamin

Answer 4

5 deoxyadenosylcobalamin and methyl cobalamin

Question 5

what reactions/enzymes require B12

Answer 5

homocysteine N-methyltransferase (Homocysteine –> Met)

and isomerization of methyl malonyl CoA (breakdown of odd chain FA and metabolism of BCAA)

Question 6

required to go from Met to Homocysteine

Answer 6

SAM for methylation reactions

other examples where SAM is needed:
Norepinephrine –> epinephrine
PE –> PC
m-RNA methylation

Question 7

To resynthesize methionine from homocysteine, what is required

Answer 7

Vit B12 and THF (tetrahydrofolate)

Question 8

what happens if deficiency in B12 in the Met-Cys cycle

Answer 8

build up of homocysteine and trapping of THF in methyl THF form

Question 9

Trapping of THF in its methyl THF form causes what…?

Answer 9

decrease of formation of other THF derivatives and impairs nucleotide synthesis as well as DNA and RNA synthesis

Question 10

what leads to homocysteinemia/homocystinuria

Answer 10

deficiency in B6 – needed for cystathione synthetase and cystathionase

deficiency in B9 (THF) - needed for homocysteine N-methyltransferase

deficiency in B12 - needed for homocysteine N-methyltransferase

Question 11

what happens in oxidation of odd chain FA if you have a deficiency in B12

Answer 11

you have a build up of methylmalonyl CoA (methylmalonyl CoA mutase needs B12) which as it accumulates turns to methylmalonyl acid —> methylmalonyl aciduria

Question 12

AA that form propionyl CoA

Answer 12

Met, Val, Ile, Thr

propionyl coA –> succinyl CoA

Question 13

effects of deficiency of B12

Answer 13

accumulation of abnormal FA –> neurological CNS effects

Question 14

what condition arises from the inability to absorb B12

Answer 14

pernicious anemia (NOT B12 deficiency) – have no intrinsic factor because of autoimmune destruction of parietal cells

Question 15

how do you treat pernicious anemia

Answer 15

lifetime intramuscular injection of cyanocobalamin (skips the absorption step)

Question 16

homocysteinemia as a result of B12 and THF deficiency can lead to…?

Answer 16

damage blood vessels –> thrombosis

lipid oxidation and increased platelet aggregation –> fibrosis and calcification of atherosclerotic plaques

Question 17

causes of B12 deficiency

Answer 17

pure vegan diet
chronic pancreatitis
terminal ileal disease

Question 18

what is megaloblastic anemia and how is it treated?

Answer 18

blood disorder with large red blood cells as a result of B12 or folic acid deficiency

treated with both folate(B9) and vit B12

Question 19

hyperhomocysteinemia is a deficiency in what

Answer 19

cystatione beta synthase

Question 20

manifestations of hyperhomocysteinemia

Answer 20

lens dislocation after age 3
osteoporosis
childhood mental retartdation
lipid deposits of atheromas

Question 21

fate of cysteine after the met-cys cycle

Answer 21

metabolized by cysteine dioxygenase to product taurine (impo for bile salt synthesis)

produce sulfate which can be excreted in urine or using ATP can form PAPs (imp for glycolipid and GAG synthesis)

Question 22

sources of folic acid (B9)

Answer 22

green leafy vegetables, liver, lima beans, whole-grain cereals

Question 23

what is the active form of folic acid and its importance

Answer 23

active form of folic acid is THF (tetrahydrofolate) and it is impo to make the other many diff form of THF which is needed for a plethora of things

Question 24

what are the THF derivates impo for?

Answer 24

DNA and RNA synthesis (purines and thymidines), some AA metabolism, synthesis of Met from homocysteine, degradation of histidine

Question 25

how do you go from folic acid to its active form THF

Answer 25

it is a 2 step reaction using dihydrofolate reductase and 2 NADPH

PS: you get folic acid from your diet but body must undergo above process in order to get the active form

Question 26

folic acid deficiency is seen in what condition

Answer 26

spina bifida (incomplete closures of neural tube)

Question 27

in microorganisms, what enzyme is inhibited in the THF formation in treatments of cancer or bacterial infection

Answer 27

dihydropteroate synthetase

Question 28

what competitively inhibits dihydropteroase synthetase and its importance

Answer 28

sulfonamides hence preventing formation of THF so no amino acid synthesis, purine synthesis, or thymidine monophosphate synthesis

PS microorganisms make their own folic acid while humans have to eat it in their diet

Question 29

in human, what enzyme is inhibited in THF formation in order to treat cancer or bacterial infection

Answer 29

dihydrofolate reductase

Question 30

what is the competitive inhibitor of dihydrofolate reductase

Answer 30

methotrexate

Question 31

Going from Ser to Gly requires what

Answer 31

THF and serine hydroxymethyltransferase

Question 32

Steps from Histidine to Glu

Answer 32

Histidine (deaminated) –> N-formiminoglutamate (FlGlu) (formimino group donated to THF) –> Glu

Question 33

what happens with degradation of histidine if there is a deficiency in THF

Answer 33

build up of FlGlu (FlGlu in urine shows deficiency in folic acid B9)

Question 34

histidinemia is a result of

Answer 34

histidinase deficiency

Question 35

folate deficiency is caused by

Answer 35

methotrexate (chemotherapeutic drug), alcohol, and sulfa drugs

Question 36

folic acid deficiency is most common in what population

Answer 36

preggo women and those leaning on that E&J

Question 37

deficiency in folic acid results in?

Answer 37

homocytinuria and megaloblastic anemia