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Energy metabolism


Energy for life

One of the main limiting factors in the life of living beings is obtaining energy for their activities. According to the heterotrophic theory, the first living beings would be heterotrophic prokaryotes living in an aquatic environment from which they would extract nutrients, formed in the atmosphere and accumulated in the lakes and early oceans.
Because of their great simplicity, these beings would use equally rudimentary processes to draw energy from these molecules they fed on. This mechanism would be similar to the fermentation still performed by many organisms today.

More than 2 billion years ago, the first autotrophic organisms emerged, prokaryotes capable of producing their own food through photosynthesis. This revolutionary process, in addition to allowing the survival of the autotrophic, also served the heterotrophic, who began to feed on them.

Photosynthesis has led to the accumulation of oxygen in the earth's atmosphere, allowing some prokaryote strains to take advantage of the oxidizing power of this molecule to draw much more energy from nutrients through respiration.

Organisms draw energy from the most diverse organic molecules (sugars, amino acids, fatty acids, etc.), but glucose It is the most common in both fermentation and respiration. For fermentation or respiration heterotrophic organisms obtain glucose if fed on the only glucose-producing photosynthetic autotrophic organisms.

Currently, only a few bacteria and fungi use the fermentation process for energy. All other organisms, whether autotrophs (algae and plants) or heterotrophs (some bacteria, fungi and protozoa and animals), use the aerobic respiration, a process of obtaining energy much more efficient than fermentation.