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Flashcards in The One Carbon Pool Deck (33)
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0
Q

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

A

TRUE

1
Q

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

A

A one-carbon pool

2
Q

What is a one-carbon carrier of carbon dioxide?

A

Biotin

3
Q

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

A

Tetrahydrofolate (THF)

4
Q

What is the principal donor of active methyl groups?

A

S-adenosylmethionine (SAM)

5
Q

Folate is a vitamin because humans cannot synthesize what?

A

Pterin ring

6
Q

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

A

Deconjugated and reduced

7
Q

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

A

In the brush border of the intestinal epithelial cells

8
Q

A cellular conjugase adds what to folate within cells?

A

Glutamate residues

9
Q

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

A

False (they can)

10
Q

True or False: 5-methyltetrahydrofolate cannot be oxidized.

A

True (it cannot be oxidized)

11
Q

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

A

Serine

12
Q

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

A

One-carbon groups

13
Q

What is used to generate SAM?

A

Methyl cycle

14
Q

What is the immediate precursor of SAM?

A

Methionine

15
Q

What is produced from hydrolysis of SAM?

A

Homocysteine

16
Q

What enzyme regenerates methionine from homocystein?

A

Homocysteine methyltransferase

17
Q

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

A

Regeneration of methionine from homocysteine

18
Q

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

A

Cystathionine

19
Q

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

A

Pyridoxal phosphate

20
Q

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

A

The methyl trap hypothesis

21
Q

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

A

Succinyl CoA

22
Q

Conversion of propionyl CoA requires what?

A

Biotin

23
Q

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

A

Methylmalonyl CoA

24
Q

What is the cofactor for methylmalonyl CoA mutase?

A

B12

25
Q

What results from a defect in methylmalonyl CoA mutase?

A

Methylmalonic aciduria

26
Q

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

A

False (it’s B12)

27
Q

What does dietary B12 bind to?

A

R-binders in the stomach

28
Q

What destroys R-binders?

A

Pancreatic proteases

29
Q

What does free B12 bind to?

A

Intrinsic factor (IF)

30
Q

Where is B12-IF complex absorbed?

A

Ileum

31
Q

B12 cirbulates as what?

A

A transcobalamin complex

32
Q

Where is B12 stored?

A

Liver