A human cell has a mutation in the gene that encodes the enzyme that generates lactate from pyruvate, rendering that enzyme completely non-functional. Assuming that there is ample glucose present, how would this cell generate energy in the presence of oxygen?

Question

A.  Glycolysis coupled with ethanol fermentation
B.  Aerobic respiration
C.  Primarily through the break down of proteins into amino acids
D.  This cell would have no way to generate energy under these conditions because it cannot carry out the reactions needed for glycolysis

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 how cells use multiple fuels to generate energy? How does this relate to the inability of the cell to convert pyruvate into lactate? 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.  Aerobic respiration

Clarify Question
What is the key concept addressed by the question?
        · The question asks you to determine how a cell that can’t convert pyruvate into lactate would be able to generate energy in the presence of oxygen if ample glucose is present.
What type of thinking is required?
        · You are being asked to dissect, or analyze, how a cell with a mutated enzyme that can convert pyruvate into lactate would be able to generate energy, considering that plenty of oxygen and glucose are present.

  Gather Content
  What do you already know about how cells use multiple fuels to generate energy? How does this relate to the inability of the cell to convert pyruvate into lactate? What other information is related to the question?
        · Recall that cells are able to use multiple fuel sources, including carbohydrates, fats, and protein, as necessary. Carbohydrates are most easily metabolized, followed by fats and then protein. The conditions under which each is metabolized during cellular respiration is largely determined by the internal and external environment and the energy needs of the cell.
        · At the end of glycolysis, cells can choose to use aerobic processes like the Krebs cycle if there is sufficient oxygen available, or they can use anaerobic processes like lactic acid fermentation when there is no oxygen. In this question, the cell has a mutation that prevents the enzyme that converts pyruvate into lactate from functioning at all. This means that lactic acid fermentation is not an option for the cell.
        · Recall that glycolysis does not depend on whether the environment is aerobic or anaerobic; however what happens to pyruvate at the end of glycolysis is dependent on environmental conditions. In this case, the question indicates there is plenty of oxygen, so downstream processes like the Krebs cycle and electron transport are possible.
   Choose Answer
  Do you have all necessary information to determine which products would affect cellular respiration?
        · Let’s try to narrow down the possible options for this question. Recall that human cells are capable of lactic acid fermentation, not ethanol fermentation. Furthermore the question indicates there is plenty of glucose available, so there would be no need to break down proteins into amino acids to derive energy for the cell. Otherwise, the cell would have no problem going through glycolysis and, if conditions are right, carrying out the Krebs cycle and electron transport to generate cellular energy.
        · The question also indicates that oxygen is present. If oxygen is present, these cells should have no problem doing aerobic respiration. Just because the cell contains a mutated enzyme and can’t convert pyruvate into lactate shouldn’t really matter, because there is plenty of oxygen around and nothing to prevent aerobic processes like the Krebs cycle and electron transport chain from functioning normally.
   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 how a human cell that has a mutated enzyme and can’t convert pyruvate into lactate would generate energy assuming ample glucose and oxygen are available.
        · If you got the correct answer, excellent! If you got an incorrect answer, were you able to remember which stages of cellular respiration require oxygen and which do not? Were you able to eliminate ethanol fermentation and protein breakdown as less likely options? Were you able to infer that the cell could still participate in aerobic respiration because there was plenty of glucose and oxygen available?