What is the Difference Between Chemiosmosis and Electron Transport Chain

The main difference between chemiosmosis and electron transport chain is that chemiosmosis uses energy in the form of a proton gradient to synthesize ATP, whereas the electron transport chain passes electrons from one molecule to another, releasing energy. 

Chemiosmosis and electron transport chain are two processes that occur in oxidative phosphorylation. 

Key Areas Covered

1. What is Chemiosmosis
– Facts, Features, Behaviour
2. What is Electron Transport Chain
– Facts, Features, Behaviour
3. Similarities Between Chemiosmosis and Electron Transport Chain
– Outline of Common Features
4. Difference Between Chemiosmosis and Electron Transport Chain
– Comparison of Key Differences

Key Terms 

Chemiosmosis, Electron Transport Chain 

What is Chemiosmosis

Chemiosmosis is the process that synthesizes ATP by the movement of protons across the inner membrane of mitochondria. It uses the integral membrane protein called ATP synthase to transport protons across the membrane. ATP synthase is also present in the thylakoid membrane of the chloroplast. However, hydrogen ions diffuse from the region of high proton concentration to the region of low proton concentration across a semipermeable membrane using the integral membrane protein ATP synthase. Importantly, the released energy is used for the synthesis of ATP.

Figure 1: Oxidative Phosphorylation in Mitochondria

Furthermore, ATP synthase contains two parts: CF0 and CF1. CF0 occurs in the thylakoid membrane, while CF1 occurs on the outer surface of the thylakoid membrane in the chloroplast. The conformational changes in the CF1 lead to the production of ATP. Additionally, NADH for obtaining energy is from the citric acid cycle that occurs in the lumen of the mitochondria. Oxidative phosphorylation occurs in mitochondria during cellular respiration. In contrast, it occurs in the chloroplast during photosynthesis. In photosynthesis, the energy of NADPH2 is the source for generating the proton gradient. It is produced in the Calvin cycle.   

What is Electron Transport Chain

The electron transport chain is a series of membrane-embedded proteins and organic molecules organized into four large complexes. They are labeled as complex I to IV. They occur in the inner mitochondrial membrane and thylakoid membrane in eukaryotes. In contrast, prokaryotes contain the electron transport chain in the plasma membrane. The significant feature of the electron transport chain is that electrons move from higher to lower energy levels across the complexes on the membrane. In eukaryotes, the two main electron donors are NADH and FADH2. Therefore, oxygen is the electron transport chain’s electron acceptor in eukaryotes.

Figure 2: Oxidative Phosphorylation in Chloroplast

Moreover, 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. Also, while transporting electrons, these complexes on the membrane transport protons from the inside to the outside of the membrane. It generates a proton gradient from the outside to the inside of the membrane.

Similarities Between Chemiosmosis and Electron Transport Chain

• Chemiosmosis and the electron transport chain are two components of oxidative phosphorylation.
• They are important for the production of ATP.
• They occur in mitochondria and chloroplast. 

Difference Between Chemiosmosis and Electron Transport Chain

Definition

Chemiosmosis refers to the movement of hydrogen ions across the membrane via ATP synthase while producing ATP. In contrast, the electron transport chain refers to a cluster of proteins that transfer electrons through a membrane within mitochondria to form a gradient of protons that drives the creation of adenosine triphosphate (ATP). 

Process

Chemiosmosis uses the proton gradient established by the electron transport chain to produce ATP, while the electron transport chain uses energy stored in NADH to produce a proton gradient.  

Integral Membrane Proteins

Chemiosmosis uses ATP synthase, while the electron transport chain uses NADH coenzyme Q reductase, coenzyme Q, succinate dehydrogenase, cytochrome bc1 complex, cytochrome c, and cytochrome c oxidase. 

Conclusion

In brief, chemiosmosis and the electron transport chain are two components of oxidative phosphorylation. Chemiosmosis uses a proton gradient established by the electron transport chain to synthesize ATP. Also, it uses the integral membrane protein ATP synthase to synthesize ATP. In comparison, electron transport chain, the energy stored in NADH produces a proton gradient. Additionally, it uses NADH coenzyme Q reductase, coenzyme Q, succinate dehydrogenase, cytochrome bc1 complex, cytochrome c, and cytochrome c oxidase as integral membrane proteins. Therefore, the main difference between chemiosmosis and electron transport chain is their process. 

References:

1. Khan Academy. (n.d.-c). Oxidative phosphorylation | biology (article). Khan Academy. 

Image Courtesy:

1. “Mitochondrial electron transport chain—Etc4” By Fvasconcellos – Own work (Public Domain) via Commons Wikimedia
2. “Thylakoid membrane 3” By Somepics – Own Work (CC-BY SA 4.0) via Commons Wikimedia