The One Carbon Pool

Question 0

True or False: In a one-carbon carrier the carbon can be in a number of oxidation states.

Answer 0

TRUE

Question 1

What are groups containing a one carbon fragment that can be transferred from one compound to another?

Answer 1

A one-carbon pool

Question 2

What is a one-carbon carrier of carbon dioxide?

Answer 2

Biotin

Question 3

Derivatives of of what, carry one-carbon units in all oxidation states except carbon dioxide?

Answer 3

Tetrahydrofolate (THF)

Question 4

What is the principal donor of active methyl groups?

Answer 4

S-adenosylmethionine (SAM)

Question 5

Folate is a vitamin because humans cannot synthesize what?

Answer 5

Pterin ring

Question 6

Prior to absorption dietary folate (folic acid) must be what? (2)

Answer 6

Deconjugated and reduced

Question 7

Processing of folate is carried out by a reductase and a conjugase where?

Answer 7

In the brush border of the intestinal epithelial cells

Question 8

A cellular conjugase adds what to folate within cells?

Answer 8

Glutamate residues

Question 9

True or False: in metabolism of folate, one carbon units cannot be interconverted.

Answer 9

False (they can)

Question 10

True or False: 5-methyltetrahydrofolate cannot be oxidized.

Answer 10

True (it cannot be oxidized)

Question 11

What is the major amino acid source of one-carbon groups among folate derivatives?

Answer 11

Serine

Question 12

Glycine, histidine, and formate are additional (serine being the primary one) sources of what among AA derivatives of folate?

Answer 12

One-carbon groups

Question 13

What is used to generate SAM?

Answer 13

Methyl cycle

Question 14

What is the immediate precursor of SAM?

Answer 14

Methionine

Question 15

What is produced from hydrolysis of SAM?

Answer 15

Homocysteine

Question 16

What enzyme regenerates methionine from homocystein?

Answer 16

Homocysteine methyltransferase

Question 17

Activated methyl from N5 - methyltetrahydrofolate and vitamin B12 (methylcobalamin) are cofactors for what reaction?

Answer 17

Regeneration of methionine from homocysteine

Question 18

Converting homocysteine to cysteine can be done in two steps. What is the intermediate product?

Answer 18

Cystathionine

Question 19

What is the cofactor in both of the two steps required to convert homocysteine to cysteine?

Answer 19

Pyridoxal phosphate

Question 20

What hypothesis explains why some macrocytic anemias respond to B12 or folate treatments?

Answer 20

The methyl trap hypothesis

Question 21

Valine, methionine, isoleucine, and threonine can be degraded to what?

Answer 21

Succinyl CoA

Question 22

Conversion of propionyl CoA requires what?

Answer 22

Biotin

Question 23

What is a common intermediate in the catabolism of valine, methionine, isoleucine and threonine?

Answer 23

Methylmalonyl CoA

Question 24

What is the cofactor for methylmalonyl CoA mutase?

Answer 24

B12

Question 25

What results from a defect in methylmalonyl CoA mutase?

Answer 25

Methylmalonic aciduria

Question 26

True or False: some forms of methylmalonyl aciduria respond to high doses of vitamin B6.

Answer 26

False (it’s B12)

Question 27

What does dietary B12 bind to?

Answer 27

R-binders in the stomach

Question 28

What destroys R-binders?

Answer 28

Pancreatic proteases

Question 29

What does free B12 bind to?

Answer 29

Intrinsic factor (IF)

Question 30

Where is B12-IF complex absorbed?

Answer 30

Ileum

Question 31

B12 cirbulates as what?

Answer 31

A transcobalamin complex

Question 32

Where is B12 stored?

Answer 32

Liver