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Human Dynamo: How Our Bodies Produce Energy

Aerobic and Anaerobic Pathways

December 25, 2012

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To sustain our daily activities we need to eat. Sounds easy enough. But where does our food go from there? How does our body produce the energy we need to walk, breathe, and keep our hearts pumping?

The macronutrients that we know, namely proteins, lipids, and carbohydrates, have a carbon skeleton that is the energy source of the foods that we eat. When these carbon-carbon and carbon-hydrogen bonds are broken through acids and metabolites in our digestive tracts, they either directly used as energy or stored as an energy source by forming other chemical bonds like the high energy bonds of adenosine triphosphate (ATP).

The main energy production in our bodies revolves around the recycling of ATP. ATP, the molecular currency of energy transfer as it is best known, is a nucleoside triphosphate that works within a cell as a coenzyme, which means it works within the cell to transport chemical energy for metabolism. Our bodies normally contain around 250mg of ATP, so it is essential that these coenzymes be recycled back to its precursors to form new ATP molecules. This process is regulated by a complex set of interactions that involves the central nervous system which senses energy needs and status.

Energy production in the form of ATP is produced by both aerobic and anaerobic pathways. The aerobic pathway produces the majorify of the energy our bodies need, with anaerobic pathways utilized under specific crucial conditions such as intense exercise and ischemia. Regeneration of ATP is crucial during strenous exercise which recruits both aerobic and anaerobic processes wherein the degree that each is used depends on the availability of oxygen.

In aerobic energy production, the tricarboxylic acid cycle (TCA cycle), or the Krebs cycle pathway plays a key role. This pathway is an important source of biosynthetic blocks used in gluconeogenesis, amino acid synthesis, and fatty acid synthesis. The Krebs cycle is a 9-step process that produces energy through the oxidation of acetyl-CoA, an ester of coenzyme A. This pathway requires oxygen to sustain its activity, specifically in the regeneration of the positive ion NAD+ which is an essential compound of the process.

Krebs Cycle
Krebs Cycle

There are at least 4 types of anaerobic pathways. Two of these pathways occur in the cytoplasm, which are gel-like substances found in the cell membrane that holds the cell's internal substructures. The other two pathways occur in the mitochondria, our "body's cellular power plants".

One of the anaerobic pathways that occur in the cytoplasm, which is called phosphagen mobilization, is the simplest form of generating ATP. One of the crucial elements of this pathway is the creatine level of the individual, since creatine phosphate (PCr) can readily transfer its phosphoryl group to ADP to form ATP:

Anaerobic Pathway: Phosphagen Mobilization
Anaerobic Pathway: Phosphagen Mobilization

For your own research, the other type of cytoplasmic anaerobic pathway is called substrate level glycolysis. The 2 types of anaerobic pathways that occurs in the mitochondria are: (1) substrate-level phosphorylation and (2) electron transport of complexes I and II as a result of reduction to succinate from fumarate.

Both aerobic and anerobic pathways of energy production contribute to fulfill all our body's range of movements.

December 25, 2012