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Can someone please explain something...you know when you calculate ATP yeild from fatty acid oxdn well say palmitic acid C16
so it is cleaved into 8 acetyl CoA i get that part-what I don't get it says (8x12) ATP produced from TCA cycle and (7x2) from FADH2 and (7x3) from NADH. BUT how is the 12 produced from the TCA cycle-from the FADH2 and NADH right?....so why have they included it twice?
Im confused -please help
Ok, so it's very simple actually. the fatty acid is cut into groups of 2 carbons that are used to make acetyl~CoA. The process itself occurs in four steps. but that doesn't matter. all you should remember is that in the process of forming each acetyl~CoA molecule from your fatty acid, aside from the acetyl-CoA molecule itself, a molecule of FADH2 and a molecule of NADH are also produced. the the acety-CoA is run through the Krebs cycle and produces an extra one ATP directly, 3 NADH and a FADH2
So for each 2 carbons of your fatty acid you get
1 acetyl-CoA which in turn makes
Considering 3 ATP/NADH and 2 ATP/FADH2 you get
2+3+(3*3)+2+1= 17 ATP molecules.
And since you took palmitic acid as an example, to find out the total ATP yield for your molecule, multiply that by 8(everything happens 8 times) and you get 136 ATP/molecule of palmitic acid.
Not out, because it's wrong
--> everything is fine until this step. Foolow the B-oxidation: every time 2 C's are cleaved to form acetyl-CoA.
Now you make THE mistake almost every students make when studying fatty acid metabolism: the last step produces 2 acetyl-CoA and thus oxidation of C16 takes place in 7 steps, not 8:
C16 --> C14 + CoA --> C12 + CoA --> C10 + CoA --> C8 + CoA --> C6 + CoA --> C4 + CoA --> 2 CoA: 7 steps B-oxidation, not 8.
Thus the nett ATP-yield of C16 is:
7 * 4 ATP = 28 ATP (FADH2 + NADH produced in B-oxidation)
10 * 8 ATP = 80 ATP (1 CoA yields 10 ATP in Krebs cycle and 8 CoA's are formed
Then you also forget the activation step.
activation = 2 ATP (formation of palmitoyl-CoA needs 2 ATP)
--> yield = 106 ATP
isn't it 12ATP's in the krebs cycle?
Also why do you do 4*7=28ATP are you just using 2atp/fadh2 and 2atp/nadh? cos my books is 2 and 3 respectively...not think it really matters anyhow...
anyway taking the activation step into consideration and also the values from my book I get a yield of 129ATP which is quite a big difference to 136 or 106
some book use 2.5 ATP/NADH and 1.5 ATP/FADH2.
So, 2.5 +1.5 = 4
In your case, they simply round it up to 3 and 2 ATP respectively.
Krebs cycle produce 3 NADH, 1 FADH2 and 1 ATP
Depending on which figure you use, you can get 12(3*3+1*2+1) or 10(3*2.5+1*1.5+1) ATP per cycle
Fatty acids are both oxidized to acetyl-CoA and synthesized from acetyl-CoA. Although the staring material of one process is identical to the product of the other, fatty acid oxidation is not the simple reverse of fatty acid biosynthesis. It is an entirely different process taking place in separate compartment of the cell. This allows each process to be individually controlled.
8 posts • Page 1 of 1
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