Lactate dehydrogenase and exhausted athletes
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Lactate dehydrogenase and exhausted athletes
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[ID] => 560287
[post_author] => 12815
[post_date] => 2025-01-12 10:02:34
[post_date_gmt] => 2025-01-12 15:02:34
[post_content] => Practice Passage (Question 1-5)
*This passage is the property of Khan Academy and has been reformatted into an AAMC-style interface in their entirety by MedLife Mastery. MedLife Mastery does not endorse and is not an affiliate of Khan Academy.
When in an oxygenated state, cells are able to generate ATP via oxidative phosphorylation. While this method of ATP production yields a much greater amount of ATP than anaerobic metabolism, it requires oxygen in order to proceed. This means that in some circumstances, anaerobic metabolism will be the preferable path to ATP formation. One example of such a circumstance is during heavy exercise, when the amount of oxygen necessary for oxidative phosphorylation exceeds the amount of usable oxygen being inhaled by the individual. In order to produce the amount of ATP necessary to continue the exercise, the body will switch to anaerobic respiration, which involves repetitive glycolysis and fermentation.
In order to exhaust the high levels of pyruvate that will accumulate from glycolysis, the enzyme lactate dehydrogenase metabolizes the pyruvate into lactic acid according to the reaction shown in Figure 1. The excess amounts of lactic acid often lead to discomfort or soreness in the areas of the body that underwent the most stress during exercise.
Figure 1. Lactate dehydrogenase converts pyruvate to L-Lactate.
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[question] => What type of enzyme is lactate dehydrogenase?
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[description] => Reason for the Correct Answer:
Lactate dehydrogenase is involved in moving a pair of electrons from one molecule to another.
Lactate dehydrogenase is reducing pyruvate and oxidizing NADH.
Lactate dehydrogenase is an oxidoreductase as it catalyzes an oxidation-reduction reaction.
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[answers] => Array
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[0] => Array
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[each_answer] => A. Transferase
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[1] => Array
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[each_answer] => B. Ligase
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[each_answer] => C. Oxidoreductase
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[3] => Array
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[each_answer] => D. Lyase
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[1] => Array
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[quiz_unique_key] => 3873426850
[question] => Which reactant/product is receiving electrons in the forward reaction shown above?
[value] => Array
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[answer] => 2
[description] => Reason for the Correct Answer:
A hydride ion is being added to pyruvate in this reaction.
Pyruvate is being reduced in this reaction.
Pyruvate is receiving electrons in the forward reaction.
)
[answers] => Array
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[0] => Array
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[each_answer] => A. L-Lactate
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[1] => Array
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[each_answer] => B. Pyruvate
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[each_answer] => C. NADH
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[each_answer] => D. NAD+
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[2] => Array
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[quiz_unique_key] => 83407773
[question] => The NAD+:NADH ratio is a component of the “redox state” of a cell. How would an increase in pyruvate concentration change this value?
[value] => Array
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[answer] => 1
[description] => Reason for the Correct Answer:
An increase in the concentration of pyruvate would increase the rate of the forward reaction.
The increase in the pyruvate concentration will increase the amount of NADH used in total.
An increase in the rate of the forward reaction will lead to more conversion of NADH to NAD+, thereby increasing the NAD+:NADH ratio.
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[each_answer] => A. It would increase the NAD+:NADH ratio since an increase in pyruvate would lead to an increase in [NAD+].
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[each_answer] => B. It would decrease the NAD+:NADH ratio since an increase in pyruvate would lead to a decrease in [NAD+].
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[each_answer] => C. It would decrease the NAD+:NADH ratio since an increase in pyruvate would lead to an increase in [NAD+].
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[each_answer] => D. It would increase the NAD+:NADH ratio since an increase in pyruvate would lead to a decrease in [NAD+].
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[question] => What would happen to the reaction free energy value shown in the passage if the L-lactate forming reaction were to occur without an enzyme?
[value] => Array
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[answer] => 1
[description] => Reason for the Correct Answer:
Enzymes increase the rate of a reaction.
Enzymes do not change the thermodynamic properties of a reaction.
Enzymes will not change the free energy of a reaction.
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[answers] => Array
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[0] => Array
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[each_answer] => A. It would not change.
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[1] => Array
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[each_answer] => B. It would increase.
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[each_answer] => C. It would decrease.
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[each_answer] => D. There is not enough information available to answer the question.
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[quiz_unique_key] => 2261298308
[question] => If a cell had a deactivating mutation in the gene coding for lactate dehydrogenase, how might that affect the cell’s concentration of NADH relative to an unmutated cell?
[value] => Array
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[answer] => 4
[description] => Reason for the Correct Answer:
NADH is being used to reduce pyruvate.
A deactivating mutation in lactate dehydrogenase would decrease the amount of NADH usage.
The cell’s relative NADH concentration would increase if less of it was being converted to NAD+ by lactate dehydrogenase.
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[each_answer] => A. The cell’s NADH concentration would remain the same.
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[each_answer] => B. The cell’s NADH concentration would decrease since less pyruvate would be converted to L-Lactate.
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[each_answer] => C. The cell’s NADH concentration would increase, since less of it was being used to oxidize pyruvate.
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[each_answer] => D. The cell’s NADH concentration would increase, since less of it was being used to reduce pyruvate.
)
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[post_title] => Lactate dehydrogenase and exhausted athletes
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