You have isolated an intact preparation of mitochondria, and add malate and ADP
ID: 64518 • Letter: Y
Question
You have isolated an intact preparation of mitochondria, and add malate and ADP + Pi. You observe the consumption of oxygen and the simultaneous production of ATP. Starting with the malate dehydrogenase enzyme in the citric acid cycle, show the steps that lead to the consumption of O2.
In a second experiment, you mechanically break open the mitochondria and repeat your experiment. In this case, you observe O2 consumption but you no longer observe ATP production. Explain why these two processes are now uncoupled.
Explanation / Answer
One characteristic of living animals is that they all give off heat. As a result of cellular respiration and cellular work, heat is produced. An operational definition of metabolism is the rate of heat production which describes the metabolic rate.
respiration
work
foodstuffs + O2
———————>
heat + ATP
———————>
heat
The direct measure of heat production, called direct calorimetry, is a technically difficult problem so an alternative method is to measure the volume of oxygen consumed or utilized by the body for ATP production. The determination of the metabolic rate from the measure of oxygen consumption is called indirect calorimetry.
Measuring oxygen consumption (VO2) under submaximal and steady-state exercise allows for estimate of the energy cost, and indirect calorimetry is the method most frequently used. This method assumes all of the energy expended for the exercise is reflected by the magnitude of VO2.
respiration
work
foodstuffs + O2
———————>
heat + ATP
———————>
heat
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