folate

[medman88]

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Just trying to make sure I understand.

1. THF-CH3 comes from food? (i.e. is this the form that's found in food or is transformed into this within the intestine)

2. Folate is only needed for the reaction that involves thymidylate synthase?

3. This question might be stupid but here goes..I know folate stores are low but why is so much used if folate is "recycled" in the reaction involving thymidylate synthase, i.e. DHF --> THF via dihydrofolate reductase

 

[medman88]

anyone? lol

 

[medman88]

got another question about this wrong, if anyone can please explain this or point me in the right direction i will be extremely grateful

 

[Boardz]

Just trying to make sure I understand.

1. THF-CH3 comes from food? (i.e. is this the form that's found in food or is transformed into this within the intestine)

2. Folate is only needed for the reaction that involves thymidylate synthase?

3. This question might be stupid but here goes..I know folate stores are low but why is so much used if folate is "recycled" in the reaction involving thymidylate synthase, i.e. DHF --> THF via dihydrofolate reductase

1. THF comes from veggies and it gets inside the body as THF. It's quickly methylated. (pathoma)
2. Folate is indeed necessary for synthesis of DNA precursors (thymine, purines) as well as methionine, glycine, f-met tRNA. (first aid)
3. We can't just recycle 100% of it. Some is inevitably lost and peed/pooed out etc. Also, demand might increase if you have a parasite inside of you (pregnancy).

 

[medman88]

1. THF comes from veggies and it gets inside the body as THF. It's quickly methylated. (pathoma)
2. Folate is indeed necessary for synthesis of DNA precursors (thymine, purines) as well as methionine, glycine, f-met tRNA. (first aid)
3. We can't just recycle 100% of it. Some is inevitably lost and peed/pooed out etc. Also, demand might increase if you have a parasite inside of you (pregnancy).

thanks for your answer def helped me sort a lot of this out,

i actually have another question regarding this...how come folinic acid (i.e. leucovorine) can be used as an antidote for MTX when the reaction seems to show that folinic acid would just be fed back into the reaction that MTX is inhibiting

 

[Boardz]

thanks for your answer def helped me sort a lot of this out,

i actually have another question regarding this...how come folinic acid (i.e. leucovorine) can be used as an antidote for MTX when the reaction seems to show that folinic acid would just be fed back into the reaction that MTX is inhibiting

Methotrexate inhibits dihydrofolate reductase, so you can't replenish the THF that you need to make DNA.

Folinic acid is converted to THF and other intermediates independent of dihydrofolate reductase- thus reversing the toxicity.

 

[medman88]

Methotrexate inhibits dihydrofolate reductase, so you can't replenish the THF that you need to make DNA.

Folinic acid is converted to THF and other intermediates independent of dihydrofolate reductase- thus reversing the toxicity.

Thanks, I've heard that before, just got confused because I haven't seen any diagrams that actually show a pathway other then folinic acid being converted to dihydrofolate...

 

[Phloston]

I had encountered a practice question at one point that asked for the only base that doesn't require folate for synthesis. The answer was cytosine.

If you look at the bottom of p. 68 and the top of p. 69 in FA, you'll see that folate is STRUCTURALLY part of purines (A and G), and it is required in the ENZYMOLOGY of thymine synthesis.

 

[Dallas]

Methotrexate inhibits dihydrofolate reductase, so you can't replenish the THF that you need to make DNA.

Folinic acid is converted to THF and other intermediates independent of dihydrofolate reductase- thus reversing the toxicity.

Also group TMP with MTX.
TMP in TMP-SMX is the equivelant of MTX but in prokaryotic cells.

Thus, if you were to give bacteria both TMP and Leucovorine it would not be as effective (id assume).

 

[Dallas]

I had encountered a practice question at one point that asked for the only base that doesn't require folate for synthesis. The answer was cytosine.

If you look at the bottom of p. 68 and the top of p. 69 in FA, you'll see that folate is STRUCTURALLY part of purines (A and G), and it is required in the ENZYMOLOGY of thymine synthesis.

What about uracil?

 

[ohyeahbaby]

What about uracil?

me thinks that you think that he was talking about thymine (methylation of uracil produces thymine)


I actually remember that annoying practice question

 

[Phloston]

Sorry, I hadn't realized I never replied here.

I would think uracil wouldn't require folate for synthesis.

The idea is that early pyrimidine synthesis, up through cytosine and uracil production, doesn't require folate. However, to get from uracil to thymine does require it, since the methylation necessitates it.

 

[ohyeahbaby]

i didn't even think about it like that... i was totally off...

very cool, thanks!