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QUIZ 8 > One Carbon Metabolism > Flashcards

One Carbon Metabolism Flashcards

1
Q

biotin

A

transfers CO2 groups

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2
Q

S-adenosylmethione (SAM)

A

transfers methyl groups

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3
Q

tetrahydrofolate (THF)

A

transfers carbon in a variety of oxidation states

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4
Q

biotin is a cofactor for _

A

pyruvate carboxylase in the formation of OAA from pyruvate

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5
Q

biotin deficiency

A

leads to defects in fatty acid synthesis, TCA cycle, ketone formation; symptoms include fatigue, depression, nausea, anemia, hair loss, heart disorders, movement disorders, and paresthesia (burning in hands)

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6
Q

biotin deficiency can be due to _

A

diet, defect in biotinidase, or defect in holocarboxylase synthetase

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7
Q

biotinidase

A

recycles biotin and releases biotin from proteins in diet

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8
Q

holocarboxylase synthetase

A

attaches biotin to the carboxylases

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9
Q

avidin

A

in egg whites and attaches to biotin to prevent it from being absorbed by intestine

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10
Q

phenytoin

A

anti-seizure drug that can lead to biotin or folate deficiency

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11
Q

vitamin B7

A

biotin

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12
Q

vitamin B9

A

folate

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13
Q

biotin is found in _

A

egg yolks, fish, meat, dairy products, nuts, potatoes, broccoli, avocados

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14
Q

folate is found in _

A

green leafy vegetables, liver, lima beans, whole grains

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15
Q

dihydrofolate reductase

A

catalyzes conversion of folate to THF

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16
Q

THF function

A

provides one carbon units for nucleotide synthesis and methylation reactions

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17
Q

folate deficiency

A

birth defects, no methylation reactions, and megaloblastic anemia

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18
Q

folate deficiency can be due to _

A

increased folate requirement (pregnancy, smoking), insufficient absorption in intestine (alcohol, certain drugs, Chron’s disease), and increased elimination (liver disease and dialysis)

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19
Q

folate deficiency symptoms

A

fatigue, gray hair, mouth sores, swollen tongue, forgetfulness, depression, low appetite, low concentration

20
Q

megaloblastic anemia

A

due to insufficient THF species for purine and thymidine synthesis; folate requirement is high in hematopoietic cells due to high division rate

21
Q

megaloblastic anemia can be caused by _

A

vitamin B9 or vitamin B12 deficiency

22
Q

How do you differentiate between vitamin B9 or B12 deficiency?

A

methylmalonic acid will be elevated in vitamin B12 deficiency

23
Q

folate antimetabolites

A

antimicrobial; also chemotherapy; enhanced with sulfanilamide

24
Q

folate cycle provides _

A

things for nucleotide metabolism and transfers methyl groups to the methionine cycle

25
Q

methionine cycle provides _

A

methyl groups for a variety of pathways

26
Q

What supplies one carbon units to the folate cycle?

A

degradation of serine, tryptophan, and histidine

27
Q

What inhibits the folate cycle?

A

SAM when there are no methyl acceptors

28
Q

methylene THF reductase

A

rate-limiting enzyme in folate-methionine bi-cycle

29
Q

How does SAM regulate its own synthesis?

A

by inhibiting methylene THF reductase

30
Q

folate cycle is required for _

A

dTMP synthesis and purine synthesis

31
Q

thymidilate synthase

A

catalyzes synthesis of dTMP from dUMP

32
Q

high DHF levels

A

switch folate cycle to DNA synthesis

33
Q

DHFR is targeted in _

A

cancer therapy

34
Q

methotrexate and aminopterin

A

folate analogs that competitively inhibit DHFR

35
Q

What happens in the absence of B12?

A

THF becomes trapped in methyl state and

36
Q

Where is vitamin B12 found?

A

animals or fortified sources (cereal)

37
Q

vitamin B12 absorption

A

pepsin in the stomach will degrade the proteins bound to B12 –> free B12 will bind to R-factor to protect from stomach acid –> proteases in small intestine will degrade R-factor and vitamin B12 will bind to intrinsic factor –> receptors in ileum will endocytose the complex

38
Q

pancreatic insufficiency

A

pancreas will not secrete proteases to digest R-factor, preventing absorption of vitamin B12

39
Q

cause of vitamin B12 deficiency

A

poor diet, infection or inflammatory condition, pernicious anemia (antibodies attack parietal cells or intrinsic factor)

40
Q

vitamin B12 deficiency leads to accumulation of _

A

homocysteine and methylmalonic acid in urine and inhibition of SAM-mediated methylation reactions and succinyl-CoA

41
Q

trans-sulfuration pathway

A

synthesizes cysteine and glutathione

42
Q

What connects the methionine cycle to the trans-sulfuration pathway?

A

homocysteine

43
Q

What can activate the trans-sulfuration pathway?

A

elevated SAM levels

44
Q

hyperhomocysteinemia

A

causes atherosclerosis, thrombosis, heart attack, stroke, dementia, epilepsy, parkinson’s, osteoporosis, eclampsia

45
Q

defect in homocystinuria

A

cystathionine beta-synthase which results in accumulation of homocysteine

QUIZ 8 (10 decks)

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