Cellular metabolism is the process of converting carbohydrates, fats, and proteins into energy needed by cells. During cellular metabolism pathways, energy is stored in the high-energy phosphate bonds of adenosine triphosphate (ATP) molecules, which serves as the cells’ energy currency. Depending on the oxygen demand during ATP production, there are two main types of metabolism present in the cell: aerobic and anaerobic. Of the three basic metabolic pathways, only glycolysis is considered an anaerobic metabolism, while the rest, including the citric acid cycle (Krebs cycle) and the electron transport chain are considered aerobic metabolisms.
Aerobic metabolism occurs only when oxygen is present. It occurs in the mitochondria of cells and is responsible for supplying 90% of the body’s energy requirements. During aerobic metabolism, all basic substrates, including carbohydrates, fats, and proteins, are broken down and combined with molecular oxygen to produce energy, releasing carbon dioxide and water as end products. There are two pathways involved in aerobic metabolism: the Krebs cycle, which occurs in the matrix of the mitochondria, and the electron transport chain, which occurs in the electron transport system located in the inner mitochondrial membrane.
Anaerobic metabolism does not require oxygen for ATP production. It occurs through glycolysis, the process by which energy is released from glucose. The efficiency of anaerobic metabolism is low because it produces a low number of ATP molecules compared to aerobic metabolism. Glycolysis occurs in the cytoplasm and does not require any organelles. Therefore, it is an important process for all those organisms without mitochondria, such as prokaryotes. The end product of aerobic metabolism is lactic acid, which can be relatively harmful to the body.
Aerobic vs. anaerobic metabolism
Contrasting aerobic metabolism with anaerobic metabolism could be misleading because, these two forms of metabolism, are not in opposition to each other but are closely related and interdependent.
Let’s take an example:
Imagine you are taking a long, leisurely walk in the park. Your body will use both aerobic and anaerobic metabolisms. Provided you’ve eaten enough that morning, are moving at a normal pace, and are not overexerting yourself, you probably won’t sweat or develop lactic acid cramping.
As long as the body’s aerobic metabolic pathways can keep up with the body’s demands, anaerobic metabolism will remain active but will take a back seat. If for some reason the energy produced by aerobic processes becomes insufficient, anaerobic processes will take on a greater role to meet the increased demand.
The key difference between the two metabolisms is that aerobic metabolism occurs in the presence of oxygen, while anaerobic metabolism does not.
We can also see this difference in the end products of the two metabolisms. In aerobic metabolism, carbon dioxide and water are produced while, in anaerobic metabolism, lactic acid (which must be disposed of) is produced.
Generally, in most cases, the negative by-products of anaerobic metabolism are not noticed because the body is able to eliminate these by-products faster than it can produce them. However, if there is an increase in intensity and greater use of anaerobic metabolism, the body will fail to eliminate lactic acid faster than it can produce it leading to the onset of cramping or, in more severe cases, metabolic acidosis.
|Does not require oxygen
|Theoretically could continue forever
|Cannot continue indefinitely
|Carbohydrates, Fats and Protein
|Involves low to moderate intensity
|Involves high intensity activities
|Where does it occur?
|In the mitochondria
|In the cytoplasm of cells
|Who produces the most energy?
|With the same amount of substrate, produces more energy aerobic metabolism
|produces less energy
|How energy production occurs
|Through the Krebs cycle and the electron transport chain
|Who contributes the most?
|Aerobic metabolism contributes the most (about 90 percent) to energy supply
|Anaerobic metabolism contributes the least
|The final product of aerobic metabolism is carbon dioxide and water
|That of anaerobic metabolism is lactic acid
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