How much of the energy released during acrobic respiration is approximately conserved in the form of ATP?
Answers
Answer:
Endergonic reactions require energy input in order to proceed (see GIBB'S FREE ENERGY). Almost every time a cell performs an endergonic reaction, such as linking amino acids, synthesizing small molecules, or cellular movement, it derives the needed energy from the splitting of ATP. Aerobic organisms produce most of their ATP through respiration, a complex set of reactions that transfer electrons from glucose to oxygen. Glycolysis is the first step in glucose metabolism. The success of glycolysis lies in its ability to couple energy releasing reactions to the endergonic synethesis of ATP.
Importance: Because ATP is considered the universal currency of biological energy, it is important to learn how cells make ATP. Also, properties of cells and chemical reactions affect the efficiency of ATP production.
Question: How can we determine the efficiency of ATP production?
Variables:
N
number of ATP molecules formed
EATP
energy in one ATP bond
Ereact
energy released in chemical reaction
Methods: The predominant source of energy in animal cells is the sugar glucose. The reaction of glucose with oxygen under standard conditions can be described by the following chemical equation:
C6H12O6 + 6O2 --> 6CO2 + 6H2O
When 1 mol (180 g) of glucose reacts with oxygen under standard conditions, 686 kcal of energy is released (DG0' = -686kcal/mol). If glucose is simply burned in air, all of this energy is released as heat. In the cell, however, this reaction is coupled to the synthesis of ATP from ADP in the following reaction:
C6H12O6 + 6O2 + 36Phosphate + 36ADP --> 6CO2 + 6H2O + 36ATP
In other words, the energy released when glucose reacts with oxygen is coupled with an endergonic reaction in order to produce ATP. However, only a fraction of the released energy goes into the high-energy bonds of ATP. Since the overall reaction is exergonic, some energy is lost as heat.
We can determine the efficiency of ATP production by comparing the energy in ATP created by the reaction to the energy released by the reaction:

where N is the number of ATP molecules formed and Ereact is the energy released as heat in the chemical reaction that is coupled with the reaction to form ATP. EATP is the energy in one high energy phophoanhydride bond in ATP, or the free energy when ATP reacts to form ADP and phosphate (ATP à ADP + phosphate).