One-Carbon Pool

Question 1

What amino acids can be degraded to succinyl CoA

Answer 1

Valine, isoleucine, methionine, threonine

Question 2

What vitamin is required for the conversion of propionyl CoA to methylmalonyl CoA

Answer 2

biotin (B7)

Question 3

What is the cofactor for methylmalonyl CoA mutase

Answer 3

methylcobalamin (B12)

Question 4

What are the cofactors for the conversion of homocysteine to methionine

Answer 4

methylcobalamin (B12) and N5 Methyl FH4 with enzyme homocysteine methyltransferase

Question 5

What is the cofactor for the conversion of homocysteine to Cysteine

Answer 5

Pyridoxal phosphate (B6), with enzymes cystathionine sythase and cystathionase

Question 6

How is FH4 converted to N5,10 methylene FH4 for recycling

Answer 6

Serine donates a methyl groups; B6 cofactor

Question 7

What does Betaine do

Answer 7

Alternate 1-carbon donor to homocysteine to convert it to methionine

Question 8

What is methylmalonic aciduria

Answer 8

Buildup of methylmalonyl CoA from defect in methylmalonyl CoA mutase. Sometimes helped by high doses of B12

Question 9

How much B12 does the liver store

Answer 9

2-5mg

Question 10

What binds B12 in the mouth and stomach

Answer 10

R-binder (haptocorrin)

Question 11

What binds B12 in the duodenum

Answer 11

Intrinsic factor

Question 12

In what form does B12 circulate in the blood

Answer 12

Transcobalamin complex

Question 13

Where does passive absorption of B12 take place

Answer 13

1% of B12 is absorbed passively in the small intestine

Question 14

In what form is tetrahydrofolate absorbed

Answer 14

Deconjugated and reduced (remove glutamates except 1 and add H to nitrogens)

Question 15

What enzyme reduces folate and what is its cofactor/hydrogen source

Answer 15

Dihydrofolate reductase; NADPH

Question 16

Why is folate a vitamin

Answer 16

Because humans cannot synthesize the pterin ring

Question 17

How is a B12 deficiency determined

Answer 17

Elevation in methyl malonyl acid

Question 18

How does homocysteine differ from cysteine

Answer 18

homocysteine has one extra carbon on its side chain

Question 19

What is the methyl trap hypothesis

Answer 19

Some macrolytic anemias respond to B12 or folate treatments because they have a build up of N5-methyl FH4, which cannot be oxidized, and requires B12 to be used

Question 20

What is the role of B7

Answer 20

It carries/transfers CO2 (most oxidized carbon)

Question 21

What does THF/FH4 do

Answer 21

carries 1-carbon groups in all oxidation states except CO2

Question 22

What is the role of SAM

Answer 22

it donates active methyl groups

Question 23

Where are the reductase and conjugate enzymes that process folate for absorption

Answer 23

They are brush border enzymes

Question 24

Where are the enzymes that reconjugate folate

Answer 24

It is a cellular conjugase

Question 25

What form of Folate cannot be oxidized

Answer 25

5-methyltetrahydrofolate