Fatty acid synthesis proceeds according to the following reaction: where n is a positive integer. Based on this, how many ADP and NADP⁺ molecules will be produced during synthesis of a 16-carbon fatty acid?

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11ecba2d_0eee_d319_a3bf_c3c791ba8426_MD0008_00 Fatty acid synthesis produces long hydrocarbon chains that are linked to a carboxylic acid. This process is facilitated by the enzyme fatty acid synthase, which successively links 2-carbon units (acetyl-CoA) to each other. The first acetyl-CoA molecule attaches directly to fatty acid synthase. Subsequent acetyl-CoA molecules are activated by combining with CO₂ to form malonyl-CoA in a reaction that requires the hydrolysis of 1 ATP molecule to form 1 ADP molecule. Malonyl-CoA is then linked to the growing fatty acid chain on fatty acid synthase, releasing CO₂ and CoA in the process. A carbonyl carbon in the chain is then reduced to the alkyl form in a process that requires oxidation of 2 NADPH molecules to form 2 NADP⁺ molecules. This process is repeated until a carbon chain of the desired length is formed. The question asks how many ADP and NADP⁺ molecules will form during synthesis of a 16-carbon fatty acid chain. The reaction scheme shows that for n + 1 acetyl-CoA molecules used, n ADP and 2n NADP⁺ molecules form. The scheme also shows that the resulting fatty acid contains 2n + 2 carbons. If the total number of carbons in the fatty acid chain (2n + 2) is 16, then 2n = 14 and n = 7. Therefore, 7 ADP molecules and 14 NADP⁺ molecules form in this process. (Choice B) Fourteen ADP and 28 NADP⁺ molecules would be produced if the fatty acid chain had 30 carbons (n = 14, 2n + 2 = 30). (Choice C) Eight ADP molecules would be produced in the formation of an 18-carbon fatty acid. In addition, fatty acid synthesis yields an even number of NADP⁺ molecules (2n), so 15 NADP⁺ molecules cannot be correct. (Choice D) Sixteen ADP and 32 NADP⁺ molecules would be produced if the fatty acid chain had 34 carbons (n = 16, 2n + 2 = 34). Educational objective: Fatty acid synthesis is the process of linking acetyl-CoA units together and reducing carbonyls to the alkyl form. To synthesize a fatty acid containing 2n + 2 carbons, n ATP molecules and 2n NADPH molecules must be consumed, forming ADP and NADP⁺.

Fatty Acid Synthesis Proceeds According to the Following Reaction