What are the steps involved in the electron transport system?

Electron transport system involves a series of processes that culminate in the synthesis of ATP. These are the four main steps of the electron transport chain: 

Step 1: Electron Transfer from NADH to Ubiquinone (UQ)

• NADH, produced in various metabolic pathways, moves from the mitochondrial matrix to the intermembrane space.
• NADH transfers electrons via Complex I (NADH dehydrogenase) to FMN in the intermembrane space, which then passes the electrons to the Fe-S centers and ultimately to CoQ, forming ubiquinol.
• The energy created during the electron transfer is used to pump two protons across the membrane, creating a potential gradient.  
• The protons return to the matrix through ATP synthase, generating energy in the form of adenosine triphosphate (ATP).

Step 2.  Electron Transfer from FADH2 to CoQ

• FADH2, produced during the oxidation of succinate to fumarate, transfers electrons via Complex II (succinate dehydrogenase) to CoQ.
• The electrons pass through a series of Fe-S centers to CoQ. No protons are pumped across the membrane.  

Step 3. Electron Transfer from CoQH2 to Cytochrome c

• The reduced CoQH2 transfers electrons to cytochrome c through cytochromes b and c1. This is facilitated by Complex III (cytochrome reductase).
• Energy from this transfer pumps protons across the membrane, enhancing the potential gradient.
• Protons return to the matrix through ATP synthase, generating energy in the form of ATP. 

Step 4: Electron Transfer from Cytochrome c to Molecular Oxygen

Complex IV (cytochrome oxidase) catalyzes the transfer of electrons from cytochrome c to molecular oxygen, reducing it to water. The energy released during this process pumps protons across the membrane back to the matrix, resulting in ATP synthesis through ATP synthase.