When we come to the end of an ATP accounting problem for a fatty acid we have to

Question

When we come to the end of an ATP accounting problem for a fatty acid we have to subtract 2 ATP equivalents. Why is that?

A. Two ATP molecules are consumed in the activation of a fatty acid.

B. This is because of unsaturation in the fatty acid.

C. Because the last product released, succinyl CoA, does not lead to as much ATP synthesis as does acetyl CoA.

D. Because in fatty acid activation, PPi is hydrolyzed to 2 Pi and this is equivalent to consuming a second ATP molecule in the activation process for the fatty acid.

Explanation / Answer

we know that

the reaction for the process is given by

Fatty acid + CoA + ATP---> Acyl CoA + AMP + 2(P)

from the above equation

we can see that

the activation of the fatty acid requires 1 molecule of ATP

now consider the breakage of ATP

ATP ---> AMP + PPi

now This PPi will break into two Pi

the reaction is

PPi --> 2 Pi

so

ultimately we get 2 Pi

because of thi reaction

it is considered that 2 ATP have been consumed in the process

so

the answer is

option D. Because in fatty acid activation, PPi is hydrolyzed to 2 Pi and this is equivalent to consuming a second ATP molecule in the activation process for the fatty acid.

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