How Does Food Energy Become Our Bodys Energy

On a daily basis we acquire energy from foods in the form of carbohydrates, protein, fat, and alcohol. However, we cannot use these molecules for energy directly. These substances must first engage in chemical reaction pathways that break them down and allow for us to capture much of their energy in a form that we can use directly. With the exception of alcohol, these food energy molecules are also stored in our body to be used as needed.

To be more specific, when these energy molecules are broken down some of their energy is captured in so-called "high-energy molecules." By far the most important high-energy molecule is adenosine triphosphate or, more commonly, ATP. Figure 1.6 displays a simplified version of ATP. When energy is needed to power an event in our body it is ATP that is used directly. So, the energy in carbohydrate is used to generate ATP, which in turn can directly power an energy-requiring event or operation in our body. As you might expect, the release of the energy from these little molecular powerhouses is controlled. Specific enzymes are employed to couple ATP with an energy-requiring chemical reaction or event and the transfer of energy.

Adenosine triphosphate (ATP) is the principal energy molecule to power body activities.

Interestingly, not all of the energy released in the breakdown of carbohydrates, protein, fat, and alcohol is incorporated in ATP. It seems that we are able to capture only about 40 to 45 percent of the energy available in those molecules in the formation of ATP. The remaining 55 to 60 percent of the energy is converted to heat, which helps us maintain our body temperature (Figure 1.7). The final product of the chemical reaction pathways that breakdown carbohydrates, proteins, fat, and alcohol is primarily carbon dioxide (CO2), which we then must exhale, and water (H2O), which helps keep our body hydrated.

Looking at the ATP molecule, we notice what looks like a phosphate

Figure 1.6 Adenosine triphosphate (ATP) is the most significant "high-energy molecule" in our body. A lot of energy is harnessed in the bonds (arrows) between the phosphates (PO4).

High-energy bonds f

High-energy bonds

Figure 1.6 Adenosine triphosphate (ATP) is the most significant "high-energy molecule" in our body. A lot of energy is harnessed in the bonds (arrows) between the phosphates (PO4).

Adenosine

40-45% of the energy is captured in phosphate bonds of ATP

Figure 1.7 Only about 40 to 45 percent of the energy released from carbohydrate, protein, fat, and alcohol is captured in the phosphate bonds of ATP and other high-energy molecules; the remaining energy is converted to heat.

tail (see Figure 1.6). Phosphate is made up of phosphorus (P) bonded to oxygen (O) and, as indicated in its name, ATP contains three phosphates. The energy liberated during the breakdown of energy nutrients is used to link phosphates together to make ATP. These phosphate links are thus little storehouses of energy. When energy is needed, special enzymes in our cells are able to break the links between adjacent phosphate groups. This releases the energy stored within that link, which can be harnessed to drive a nearby energy-requiring reaction or process.

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