Mezo
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Hey guys,
I was solving kaplan q-bank bio ... where they asked about net energy from B-oxidation ..
The q was =>
Starting with a 12 carbon FA, what is the net energy yield in high-energy phosphate bonds from each molcule of this FA ????
and the choices were =>
83 , 85 , 95 , 97 , 110
I Calculated it and i didn't get any of these nos. i got 87 ?? and i couldn't understand the explanation .... so could anyone explain to me???
Here is how i calculated it = >
B-oxidation removes 2 carbons from the FA / cycle ... then it would do 5 cycles as the the 5th will release 2 Acetyl CoA instead of 1 ( it releases 1/cycle and 1 is left in the original molecule ) ....
Net Energy of Each cycle = >
- - 2 Bonds lost to activate the FA to FA-CoA ( ATP -> AMP )
- +1 FADH2
- +1 NADH
- +1 Acetyl CoA
So the nest energy should be =>
5 cycles x -2 bonds = -10 bonds
-----------x +1FADH2 = +5 FADH2 each yields 2ATPs / ETC cycle = +10 ATPs
-----------x +1NADH = +5 NADH -------------- 3 ATPs / ETC cycle = +15 ATPS
6 Acetyl Co As => each 1 entering Krebs cycle yields 3 NADHs , 1 FADH2 & 1 GTP =>
----------x 3 NADHs = 18 NADHs each of which yileds3 ATPs / ETC = + 54 ATPs
----------x 1 FADH2 = 6 FADH2s ---------------------------2 ATPs / ETC = +12 ATPs
----------x 1 GTP = 6 GTPs
Net Total = - 10 + 10 + 15 + 54 + 12 + 6 = 87
So, what i did wrong ???
could anyone explain to me ???
And do u think this type of qs can be seen on the exam???
Thanks a lot for ur time and support
Edited by Mezo on 03/12/08 - 05:47 AM
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| tia
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hi mezo ia the answer 85??? if not just paste the explanation they gave
and yeah such questions are asked i found them qite often
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| genbot
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mezo the answer is 95. You only need to activate the FA once, that is before entering the mitochondria. Once it is inside no further ATPs are required. That is activation is not cyclic but occurs only once. So instead of 10 subtract only 2, which gives you the answer 95.
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| Mezo
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Yes, u right Genbot, that's what i missed ... thanks a lot ....
And i found a formula that makes it a piece of cake ....
ATPs derived from B-oxidation of FA = >
n = no. of Carbons while N = n/2
ATP = (12 x N ) + ( 5 x {N - 1} ) - 2
I found this Formula in the Biochemistry support forum here in the Mnemonic section ... I don't what its source, but it actually works and saves alot of time ... if this kind of qs u can c on the exam ... then i think using this formula will help a lot ...
Thanks genbot and tia for ur help
Edited by Mezo on 03/12/08 - 06:57 AM
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| genbot
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Hey mezo i think the formula should be 12*N, not 2*N. Cause 12 ATPs are derived from each acetyl CoA.
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| Mezo
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Yes genbot, u r again right   ... it was a typo error ... sorry for that, i corrected it ...
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| tia
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hey genbot thanks ... wanted to ask u meanwhile i saw ur reply thats why say u rock dude
@ mezo good question made me think thanks mezo
mezo its 12 ...u typed in a hurry i guess u were happy to get the answer after u broke ur head so much time....i was not getting the answer with the formula so went and checked it biochem suppot forum but thanks for the formula saves a lot of time
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| Mezo
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U r welcome tia, but i thought u went over it b4, sice u done with bio i think ???
And I corrected it , b4 u reply again, check above, it was atypo error ..
and how did u find the mnemonics ?? i liked them so much, especially the one for FABRY'S disease ...
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| genbot
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Thanks guys. Could answer only because i'm finished with the prep and you're still on your way there. Nothin more to it. These are good questions you know. Test your concepts thoroughly. If you can master them then you're game for anything!
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| Mezo
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don't thank us genbot we r the ones who are Honored to have u here, believe me ...
Anyway, I'd like to ask u another thing, i keep mixing Lipid storage diseases with glycogen storage diseases ... could u help me overcome this, I mean, did u used a special mnemonic device or had figure out key clues for every disease??? I'll be glad if u shared with us ...
Thanks for your time.
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| genbot
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No buddy i used no special method here. Just plain memorization. But generally speakin they dont ask you a question which says, 'Is this a lipid or a glycogen storage disease?' What they do expect you to know is that you recognize each disease entity separately. Revise enough and do enough questions and you'll soon have them sorted.
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| Mezo
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Thanks a lot genbot
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| bhanusupriya
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very useful point,
thanks to MEZO , TIA and GENBOT
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| ShweHope99.9998
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Thanks Mezo for bring this Q up
Thanx GB , for clear up the problem .
GL GL GL happy success study to us , all
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