If you take into account the amount of ATP generated by ATP synthase per molecule of NADH produced in aerobic respiration, the net number of ATP molecules produced by substrate-level phosphorylation, and the fact that NADH molecules produced in the cytoplasm have to be transported into the mitochondria, what is the predicted energy yield of glycolysis in eukaryotic cells?

Question

A.  2 ATP
B.  5 ATP
C.  7 ATP
D.  32 ATP
E.  30 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 glycolysis and ATP and NADH yield? What energy costs are required to transport NADH produced in the cytosol via glycolysis into the mitochondria? What other information is related to the question?
   Choose Answer
  Do you have all necessary information to determine which products would affect cellular respiration?

  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

B.  5 ATP

Clarify Question
What is the key concept addressed by the question?
        · The question asks you to determine the predicted yield of glycolysis from associated NADH molecules and net ATP produced. 
What type of thinking is required?
        · You are being asked to dissect, or analyze, glycolysis for ATP and NADH production to determine the total yield of ATP during glycolysis.

  Gather Content
  What do you already know about glycolysis and ATP and NADH yield? What energy costs are required to transport NADH produced in the cytosol via glycolysis into the mitochondria? What other information is related to the question?
        · Recall that the first part of cellular respiration is glycolysis, which occurs in the cytosol. Products from glycolysis include ATP and NADH, among other molecules.
        · Glycolysis requires energy investment, which takes away from the total number of ATP it can produce via substrate-level phosphorylation. NADH, another key product of glycolysis, holds high energy electrons that can ultimately be used to produce ATP via chemiosmosis and oxidative phosphorylation in the mitochondria using ATP synthase during electron transport.
        · How many ATP molecules can conceivably be produced in the mitochondria from one NADH molecule?
   Choose Answer
  Do you have all necessary information to determine which products would affect cellular respiration?
        · Remember that during glycolysis 4 total ATP are produced, 2 ATP need to be invested in the early stages, leaving a net of 2 ATP molecules produced overall. In addition, 2 molecules of NADH are produced during glycolysis.
        · Each molecule of NADH, whether made in the cytosol or in the mitochondria, will deposit their high-energy electrons into the electron transport chain. ATP synthase, the key enzyme that produces ATP via the chemiosmotic proton gradient, is predicted to yield 2.5 molecules of ATP per NADH molecule. Thus, during glycolysis, we generate 2 net ATP via substrate-level phosphorylation and another 5 for the 2 molecules of NADH that are produced.
        · However, each molecule of NADH generated by glycolysis has to be transported into the mitochondria via active transport, which requires 1 ATP molecule per NADH to be transported.
        · Therefore, the total energy yield of glycolysis in a eukaryotic cell should be: 2 ATP (glycolysis net ATP) + 5 ATP (2 NADH molecules from glycolysis making 2.5 ATP each during chemiosmosis) - 2ATP (NADH active transport into mitochondria) = 5 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 analyze the different ways that ATP could be produced both during glycolysis as well as from glycolytic products and to account for the ATP costs across the board.
        · If you got the correct answer, well done! If you got an incorrect answer, were you able to accurately tally how many ATP were made via substrate-level phosphorylation in glycolysis? Did you consider how many ATP could be produced from the NADH molecules produced during glycolysis? Did you account for the energy costs associated with glycolysis itself as well as NADH active transport into the mitochondria?