Cardiac muscle cells need to generate significant amounts of ATP to allow for constant contractile activity. As a result, they primarily depend upon beta-oxidation of fatty acids, which has a higher energy yield than the catabolism of glucose. What would be the ATP yield for beta-oxidation of a hypothetical 10-carbon fatty acid?

Question

A.  32 ATP
B.  35 ATP
C.  50 ATP
D.  62 ATP
E.  65 ATP

Clarify Question
What is the key concept addressed by the question?
What type of thinking is required?

  Gather Content
  What do you already know about cellular respiration and beta-oxidation of fatty acids? How do these molecules plug into the process of cellular respiration? What other information is related to the question?
   Choose Answer
  Do you have all necessary information to determine the ATP yield from beta-oxidation of a 10-carbon fatty acid?
   Reflect on Process
  Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

D.  62 ATP

Clarify Question
What is the key concept addressed by the question?
        · The question asks you to determine the ATP yield for beta-oxidation of a 10-carbon fatty acid.
What type of thinking is required?
        · You are being asked to use what you already know about beta-oxidation of fatty acids and use it to determine, or analyze, the ATP yield for a 10-carbon fatty acid.

  Gather Content
  What do you already know about cellular respiration and beta-oxidation of fatty acids? How do these molecules plug into the process of cellular respiration? What other information is related to the question?
        · Recall that cellular respiration is a process of oxidizing glucose and other organic molecules in order to produce NADH and ultimately the ATP used to power cellular processes. Respiration is comprised of glycolysis, pyruvate oxidation, the Krebs cycle, and electron transport.
        · Recall that molecules other than glucose are metabolized for energy in cells; this includes breakdown of fatty acids and glycerol and, in certain circumstances, proteins into amino acids. Each of these molecules plugs into cellular respiration in different places and under different conditions. The process of breaking down fatty acids is called beta-oxidation and involves cutting fatty acid into two carbon fragments (acetyl-CoA) that plug into the Krebs cycle.
   Choose Answer
  Do you have all necessary information to determine the ATP yield from beta-oxidation of a 10-carbon fatty acid?
        · For each round of the Krebs cycle, the ATP yield is 10 ATP. To calculate the 10 ATP, remember that 3 NAD molecules are produced per turn of the Krebs cycle. If you multiply that by the 2.5 ATP that can be produced via ATP synthase per NADH molecule, and you add that to both the one FADH2 molecule that is also produced during one turn of the Krebs cycle (which itself produces 1.5 ATP via ATP synthase) and the one ATP produced via substrate-level phosphorylation, then you get something that looks like this: ((3 NADH*2.5 ATP)+(1 FADH2*1.5 ATP)+1 ATP via substrate-level phosphorylation) = 10 ATP.
        · For each round of beta-oxidation, 1 molecule of ATP is invested, and 1 molecule of NADH and FADH2 are generated. This means that for each round of beta-oxidation, 3 ATP are generated. For a 10-carbon fatty acid, there would be 4 rounds of beta-oxidation to cleave a 10-carbon molecule into 5 2-carbon molecules. Thus, from beta-oxidation there would be a yield of 12 ATP.
        ·Each of these 5 2-carbon acetyl-CoA molecules could enter the Krebs cycle; thus the Krebs cycle will run 5 times for a total yield of 50 ATP. Taken together, the oxidation of a 10-carbon fatty acid would yield 62 ATP.
   Reflect on Process
  Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        · Answering this question correctly depended on your ability to remember how beta-oxidation works during cellular respiration and use that to analyze the ATP yield of a 10-carbon fatty acid.
        · If you got the correct answer, well done! If you got an incorrect answer, were you able to recall how beta-oxidation of fatty acids works? Were you able to correctly calculate how many NADH and FADH2 molecules would be produced from a single 2-carbon fragment from a fatty acid and a turn of the Krebs cycle? Were you able to determine the total number of ATP from beta-oxidation reactions, ATP synthase-generated ATP from NADH and FADH2, and ATP made via substrate-level phosphorylation?