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Old 09-11-2011
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Biochemistry 12-Carbon Fatty Acid Oxidation!

A person eats cookies made with coconut oil. The predominant fatty acid in the triglycerides contained in the coconut oil is lauric acid, which is a saturated 12-carbon fatty acid. Starting with free lauric acid, what is the net energy yield in high-energy phosphate bonds from each molecule of lauric acid?
a. 83
b. 85
c. 95
d. 97
e. 110

plz with explanation
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Old 09-11-2011
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We are talking about β-oxidation of a saturated fatty acid with even number of carbons (saturated 12-carbon fatty acid).
β-oxidation consists of a sequence of four reactions (consult a biochemistry textbook) that results in shortening the fatty acid chain by two carbons.
This goes on for (n/2) - 1 times (n = number of carbons). That is 12/2 - 1 = 5 times.
Products are 1 FADH2, 1 NADH and 1 acetyl CoA for each time. So we have 5 FADH2, 5 NADH and 5 acetyl CoA plus the 1 acetyl CoA remaining, so 6 acetyl CoA.
In oxidative phosphorylation, 1 FADH2 provides 2 ATP, 1NADH 3ATP. At TCA cycle each acetyl CoA provides 12 ATP when converted to CO2 and H20. So 5x2 + 5x3 + 6x12 = 97 ATP
Now, don't forget that activation of a fatty acid requires 2 ATP.
Finally, 97 - 2 = 95 ATP. Thus, i would go for C.

I tried to write it as concise as possible. I consulted neither Kaplan nor UW. Just LIR: Biochemistry.
Hope it helps!!!

Last edited by Relid; 09-11-2011 at 10:06 PM.
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Old 09-11-2011
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Quote:
Originally Posted by sat_md View Post
We are talking about β-oxidation of a saturated fatty acid with even number of carbons (saturated 12-carbon fatty acid).
β-oxidation consists of a sequence of four reactions (consult a biochemistry textbook) that results in shortening the fatty acid chain by two carbons.
This goes on for (n/2) - 1 times (n = number of carbons). That is 12/2 - 1 = 5 times.
Products are 1 FADH2, 1 NADH and 1 acetyl CoA for each time. So we have 5 FADH2, 5 NADH and 5 acetyl CoA plus the 1 acetyl CoA remaining, so 6 acetyl CoA.
In oxidative phosphorylation, 1 FADH2 provides 2 ATP, 1NADH 3ATP. At TCA cycle each acetyl CoA provides 12 ATP when converted to CO2 and H20. So 5x2 + 5x3 + 6x12 = 97 ATP
Now, don't forget that activation of a fatty acid requires 2 ATP.
Finally, 97 - 2 = 95 ATP. Thus, i would go for C.

I tried to write it as concise as possible. I consulted neither Kaplan nore UW. Just LIR: Biochemistry.
Hope it helps!!!
thanks so much it is so clear i had my first read of kaplan bio from about 2 weeks but when i meet questions on bio while i am studying immuno now i got trouble with them or go back to the book ,, is that normal for the first read or i am not doing it right?? ,, thanks so much for your help
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Old 09-11-2011
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What is the source of this question mentallah?
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Old 09-11-2011
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Default No worries

Mentallah Elgohary, of course it's normal! Happens to everyone. At least it happens to me...
If it's not, would be better for everyone to sit for the exam right away after first read... Believe me it's not happening. And if it is, it's extremely rare.
So don't worry. Keep studying as you do... Everything is going to be fine!

Last edited by Relid; 09-12-2011 at 06:01 AM.
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Old 09-12-2011
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Quote:
Originally Posted by Crimsonboy View Post
What is the source of this question mentallah?
there is kaplan Q bank appilication on facebook everyday you have 3 questions with answers
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Old 09-12-2011
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Quote:
Originally Posted by sat_md View Post
Mentallah Elgohary, of course it's normal! Happens to everyone. At least it happens to me...
If it's not, would be better for everyone to sit for the exam right away after first read... Believe me it's not happening. And if it is, it's extremely rare.
So don't worry. Keep studying as you do... Everything is going to be fine!
thanks sooo much
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