One Carbon Metabolism

Question 1

biotin

Answer 1

transfers CO2 groups

Question 2

S-adenosylmethione (SAM)

Answer 2

transfers methyl groups

Question 3

tetrahydrofolate (THF)

Answer 3

transfers carbon in a variety of oxidation states

Question 4

biotin is a cofactor for _

Answer 4

pyruvate carboxylase in the formation of OAA from pyruvate

Question 5

biotin deficiency

Answer 5

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)

Question 6

biotin deficiency can be due to _

Answer 6

diet, defect in biotinidase, or defect in holocarboxylase synthetase

Question 7

biotinidase

Answer 7

recycles biotin and releases biotin from proteins in diet

Question 8

holocarboxylase synthetase

Answer 8

attaches biotin to the carboxylases

Question 9

avidin

Answer 9

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

Question 10

phenytoin

Answer 10

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

Question 11

vitamin B7

Answer 11

biotin

Question 12

vitamin B9

Answer 12

folate

Question 13

biotin is found in _

Answer 13

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

Question 14

folate is found in _

Answer 14

green leafy vegetables, liver, lima beans, whole grains

Question 15

dihydrofolate reductase

Answer 15

catalyzes conversion of folate to THF

Question 16

THF function

Answer 16

provides one carbon units for nucleotide synthesis and methylation reactions

Question 17

folate deficiency

Answer 17

birth defects, no methylation reactions, and megaloblastic anemia

Question 18

folate deficiency can be due to _

Answer 18

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

Question 19

folate deficiency symptoms

Answer 19

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

Question 20

megaloblastic anemia

Answer 20

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

Question 21

megaloblastic anemia can be caused by _

Answer 21

vitamin B9 or vitamin B12 deficiency

Question 22

How do you differentiate between vitamin B9 or B12 deficiency?

Answer 22

methylmalonic acid will be elevated in vitamin B12 deficiency

Question 23

folate antimetabolites

Answer 23

antimicrobial; also chemotherapy; enhanced with sulfanilamide

Question 24

folate cycle provides _

Answer 24

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

Question 25

methionine cycle provides _

Answer 25

methyl groups for a variety of pathways

Question 26

What supplies one carbon units to the folate cycle?

Answer 26

degradation of serine, tryptophan, and histidine

Question 27

What inhibits the folate cycle?

Answer 27

SAM when there are no methyl acceptors

Question 28

methylene THF reductase

Answer 28

rate-limiting enzyme in folate-methionine bi-cycle

Question 29

How does SAM regulate its own synthesis?

Answer 29

by inhibiting methylene THF reductase

Question 30

folate cycle is required for _

Answer 30

dTMP synthesis and purine synthesis

Question 31

thymidilate synthase

Answer 31

catalyzes synthesis of dTMP from dUMP

Question 32

high DHF levels

Answer 32

switch folate cycle to DNA synthesis

Question 33

DHFR is targeted in _

Answer 33

cancer therapy

Question 34

methotrexate and aminopterin

Answer 34

folate analogs that competitively inhibit DHFR

Question 35

What happens in the absence of B12?

Answer 35

THF becomes trapped in methyl state and

Question 36

Where is vitamin B12 found?

Answer 36

animals or fortified sources (cereal)

Question 37

vitamin B12 absorption

Answer 37

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

Question 38

pancreatic insufficiency

Answer 38

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

Question 39

cause of vitamin B12 deficiency

Answer 39

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

Question 40

vitamin B12 deficiency leads to accumulation of _

Answer 40

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

Question 41

trans-sulfuration pathway

Answer 41

synthesizes cysteine and glutathione

Question 42

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

Answer 42

homocysteine

Question 43

What can activate the trans-sulfuration pathway?

Answer 43

elevated SAM levels

Question 44

hyperhomocysteinemia

Answer 44

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

Question 45

defect in homocystinuria

Answer 45

cystathionine beta-synthase which results in accumulation of homocysteine