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Biochem Exam 2 TonyFrim > One Carbon Metabolism > Flashcards

One Carbon Metabolism Flashcards

1
Q

Carbon source for SAM?

A

Methionine

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2
Q

Carbon source for Biotin

A

CO2

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3
Q

How many methylation reactions does FH4 participate in

A

Only one methylation reaction, all others use SAM

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4
Q

Biotin is the cofactor for what 3 major carboxylases

A

Pyruvate carboxylase, Acetyl CoA carboxylase, and Propionyl Carboxylase

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5
Q

What is the first enzyme in fatty acid synthesis

A

Acetyl CoA carboxylase

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6
Q

Pyruvate carboxylase is the first enzyme in what metabolic pathway?

A

Gluconeogenesis

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7
Q

One way to get biotin deficiency…

A

eat 20 raw egg whites in one day

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8
Q

In biotin carboxylase, where is biotin attached

A

to the Epsilon amino group of lysine

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9
Q

Biotinidase is present in cells and serum, and it cleaves biotin from

A

proteins

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10
Q

Holocarboxylase synthetase deficiency can result in

A

encephalopathic crisis (brain damage) and hair loss

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11
Q

SAM is synthesized in a reaction involving both

A

Methionine and ATP

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12
Q

SAM is a major carrier of ________ groups in metabolism

A

methyl

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13
Q

Two possible fates of homocysteine

A

Homocysteine is converted to methionine or used in cysteine synthesis

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14
Q

S-Adenosyl homocysteine is hydrolyzed to

A

adenosine and homocysteine

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15
Q

What is the MAJOR carrier of C1 groups in metabolism?

A

Tetrahydrofolate (FH4)

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16
Q

FH4 is a reduced form of

A

folic acid

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17
Q

What can synthesize folate

A

Not humans. Bacteria and higher plants synthesize folate

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18
Q

Why do pregnant women supplement with folic acid?

A

To prevent neural tube defects

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19
Q

Folate is converted to FH4 by 2 reactions with what one enzyme?

A

dihydrofolate reductase in an NADPH dependent reaction

20
Q

What body organ stores about half of the body’s FH4?

A

liver

21
Q

What form is folate absorbed in by the small intestines?

A

Monoglutamate

22
Q

What two positions do C1 units bind to on FH4?

A

N5 and/or N10

23
Q

Formyl groups bind _____, methyl groups bind ____, while Methenyl and methylene groups form carbon bridges between

A

N10
N5
N5 and N10

24
Q

Most C1 acceptors are intermediates in

A

purine and pyrimidine synthesis

25
Q

All FH4 derivaties are easily interconverted, reversible reactions, except

A

N-5-methyl-FH4 (energetically stable)

26
Q

Dietary sources of folic acid

A

Green vegetables, yeast, liver, some fruits

27
Q

oversized RBC precursors in bone marrow (subtype of macrocytic anemia)

A

Megaloblasts

28
Q

Analog to folic acid which inhibits dihydrofolate reductase which converts dihydrofolate to tetrahydrofolate

A

Methotrexate

29
Q

Methotrexate stops cell

A

division of rapidly dividing tumor cells

30
Q

B12 (cobalamin) contains

A

cobalt

31
Q

What are the two B12 dependent reactions in humans?

A

Homocysteine–>Methionine

Methylmalonyl CoA–> Succinyl CoA (required for BCAA metabolism)

32
Q

What are the basic major sources of B12?

A

Meat and dairy are the major sources of B12

33
Q

Proteases release B12 from proteins and then it is bound by

A

haptocorrins (R-binders)

34
Q

Proteases release B12 from haptocorrins and then it is bound to …

A

Intrinsic factor

35
Q

Reduced amounts of Intrinsic factor cause

A

pernicious anemia (common in elderly)

36
Q

What is the most energetically stable form of carbon FH4?

A

N5-methyl -FH4 (it cannot be converted to other forms of FH4)

37
Q

What cofactor is required for the only reaction that can remove CH3 from N5methylFH4

A

Vit B12

38
Q

Lack of B12 causes increase in ___________ and reduces pool of ________

A

homocysteine

FH4

39
Q

folate is “trapped” in N5-methyl form

A

Methyl Trap Hypothesis

40
Q

What cofactor is required in the BCAA degradation reaction of methylmalonyl CoA to succinyl CoA

A

Vitamin B12

41
Q

too much homocysteine in the blood

A

Hyperhomocysteinemia

42
Q

_______ in the liver is an alternate pathway for homocysteine to Methionine

A

Betaine

43
Q

High levels of homocysteine can result from what 3 possibilities?

A

1) Folate deficiency 2)B12 deficiency 3) mutation in cystathione beta synthase

44
Q

Mutations in cystathione beta synthase cause____________, which is a rare extreme of hyperhomocysteinemia and its symptoms resemble

A

homocystinuria…. Marfan

45
Q

Major difference between B12 deficiency and folate deficiency

A

B12 deficiency has neurological symptoms which are not present in folate deficiency

46
Q

Megaloblasts form in the

A

bone marrow

47
Q

B12 and folate deficiency can both cause

A

megaloblastic anemia

Biochem Exam 2 TonyFrim (4 decks)

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