What is the Difference Between Electron Transport Chain in Prokaryotes and Eukaryotes

The main difference between electron transport chain in prokaryotes and eukaryotes is that the electron transport chain of the prokaryotes occurs in the plasma membrane whereas the electron transport chain of eukaryotes occurs in the inner membrane of the mitochondria.

The electron transport chains of the prokaryotes and eukaryotes are a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions, coupling the electron transfer with the transfer of protons (H+ ions) across a membrane. Moreover, the electron transport chain is a pathway of cellular respiration.

Key Areas Covered

1. What is Electron Transport Chain in Prokaryotes
   • Definition, Characteristics, Importance
2. What is Electron Transport Chain in Eukaryotes
   • Definition, Characteristics, Importance
3. Similarities Between Electron Transport Chain in Prokaryotes and Eukaryotes
   • Outline of Common Features
4. Difference Between Electron Transport Chain in Prokaryotes and Eukaryotes
   • Comparison of Key Differences

Key Terms

Cellular Respiration, Electron Transport Chain, Eukaryotes, Prokaryotes

What is Electron Transport Chain in Prokaryotes

The electron transport chain in prokaryotes is a series of proteins that transfer electrons through a membrane to create a gradient of protons. Prokaryotes generally do not contain membrane-bound organelles such as mitochondria; therefore, their cellular respiration processes including glycolysis and Calvin cycle occur in the cytoplasm. In the meanwhile, the electron transport chain of prokaryotes occurs in the inner plasma membrane.

Figure 1: Anaerobic Denitrification

Furthermore, there are several electron donors and electron acceptors in the prokaryotic electron transport chain. However, the main feature of prokaryotes is the use of inorganic matter as their electron sources. They are chemolithotrophs. Some of the inorganic electron donors include hydrogen, carbon monoxide, ammonia, nitrite, sulfur, sulfide, manganese oxide, and ferrous iron. In addition, electrons can enter three levels: at the dehydrogenase level, in the quinone pool, and at the cytochrome level. Moreover, electron acceptors in prokaryotes can be nitrate, fumarate, sulfate, or elemental sulfur. Therefore, prokaryotes undergo anaerobic respiration as oxygen is not the final electron acceptor.

What is Electron Transport Chain in Eukaryotes

The electron transport chain in eukaryotes is a series of protein complexes located in the inner mitochondrial membrane. Unlike prokaryotes, eukaryotes contain mitochondria, the membrane-bound organelles that conduct cellular respiration. The function of mitochondria is to react oxygen with the products of the citric acid cycle, fatty acid metabolism, and amino acid metabolism to produce ATP.

Figure 2: Electron Transport Chain of Eukaryotes

In eukaryotes, the two main electron donors are NADH and FADH₂. They pass electrons to oxygen and energy for the driving of the process given by the reduction of oxygen. Therefore, oxygen is the electron acceptor of the electron transport chain of eukaryotes. On the other hand, the electrons of the donor pass through a series of protein complexes; complex I, quinone, complex III, cytochrome c, and complex IV. Here, the complex IV transfer electrons to oxygen. Since oxygen is the final electron acceptor, eukaryotes undergo aerobic respiration. In addition, complex I is the NADH dehydrogenase, complex II is the succinate dehydrogenase, complex III is the quinone-cytochrome c reductase, and complex IV is cytochrome c oxidase.

Similarities Between Electron Transport Chain in Prokaryotes and Eukaryotes

• The electron transport chains of prokaryotes and eukaryotes are pathways of cellular respiration.
• They are a series of proteins and other molecules.
• In these pathways, electrons are transferred from donors to acceptors.
• The electron transfer of these pathways is coupled with proton transfer.
• The main function of the electron transport chain is to generate ATP.

Difference Between Electron Transport Chain in Prokaryotes and Eukaryotes

Definition

The electron transport chain of prokaryotes refers to a cluster of proteins that transfer electrons through the plasma membrane to create a gradient of protons while the electron transport chain in eukaryotes is the transfer of electrons through the mitochondrial membrane to create a proton gradient.

Occurrence

Usually, the electron transport chain of prokaryotes occurs in the inner plasma membrane while the electron transport chain of eukaryotes occurs in the inner mitochondrial membrane.

Type of Respiration

Prokaryotes undergo anaerobic respiration while eukaryotes undergo aerobic respiration.

Dehydrogenase Complexes

The eukaryotic electron transport chain contains NADH dehydrogenase and succinate dehydrogenase while the prokaryotic electron transport chain uses other dehydrogenases such as lactate dehydrogenase, formate dehydrogenase, H2 dehydrogenase, etc.

Electron Donors

Inorganic matter (hydrogen, carbon monoxide, ammonia, nitrite, sulfur, sulfide, manganese oxide, and ferrous iron) is the electron donors and electron acceptors are nitrate, fumarate, sulfate, or elemental sulfur in the prokaryotic electron transport chain while organic matter (NADH and FADH₂) are the electron donors and, oxygen is the electron acceptor in the eukaryotic electron transport chain.

Conclusion

In brief, the electron transport chain of prokaryotes and eukaryotes is a series of proteins and other molecules that produce ATP. For that, they use the energy in electrons to reduce electron acceptors coupled to proton transfer across the membrane. The prokaryotic electron transport chain occurs at the inner plasma membrane while the eukaryotic electron transport chain occurs at the inner membrane of mitochondria. Since prokaryotes use anaerobic respiration and eukaryotes undergo aerobic respiration, the electron donors and acceptors as well as the enzymes used in the electron transport chain are different. However, the main difference between electron transport chain of prokaryotes and eukaryotes is the location where they occur.

References:

1. Electron Transport Chain. Lumen. Retrieved September 15, 2022.

Image Courtesy:

1. “Mitochondrial electron transport chain—Etc4” By Ijeoma Obi – Own work (Public Domain) via Commons Wikimedia
2. “Anaerobic Denitrification (ETC System)” By Fvasconcellos- Own Work (CC By-SA 4.0) via Commons Wikimedia