Respiratory chain

Respiratory chain

The respiratory chain also known as the electron transport chain is a series of protein complexes and lipid soluble carriers found on the inner mitochondrial membrane that are involved in the process of cellular respiration. The respiratory chain is responsible for the oxidative phosphorylation, where the energy released by electrons is used to create a proton gradient across the inner mitochondrial membrane. This gradient is then used to drive the synthesis of adenosine triphosphate (ATP), the cell's main energy currency.

Function

The respiratory chain is the final stage of cellular respiration, following glycolysis and the Krebs cycle. It is where the majority of the ATP is produced. The process involves the transfer of electrons from NADH and FADH2, produced in the Krebs cycle, to oxygen, producing water. This transfer of electrons is coupled with the pumping of protons (H+) across the inner mitochondrial membrane, creating a proton gradient. The energy stored in this gradient is then used to drive the synthesis of ATP by the enzyme ATP synthase.

Components

The respiratory chain consists of four protein complexes, named Complex I to IV, and two mobile electron carriers, coenzyme Q and cytochrome c. Each complex is involved in the transfer of electrons and the pumping of protons across the membrane.

Complex I

Also known as NADH:ubiquinone oxidoreductase, Complex I is the first complex in the respiratory chain. It accepts electrons from NADH and transfers them to coenzyme Q. This process is coupled with the pumping of four protons across the membrane.

Complex II

Complex II, or succinate:ubiquinone oxidoreductase, is the only complex not involved in the pumping of protons. It accepts electrons from FADH2, produced in the Krebs cycle, and transfers them to coenzyme Q.

Complex III

Complex III, or ubiquinol:cytochrome c oxidoreductase, accepts electrons from coenzyme Q and transfers them to cytochrome c. This process is coupled with the pumping of four protons across the membrane.

Complex IV

The final complex, Complex IV or cytochrome c oxidase, accepts electrons from cytochrome c and transfers them to oxygen, producing water. This process is coupled with the pumping of two protons across the membrane.

See also

• Mitochondrion
• Cellular respiration
• Oxidative phosphorylation
• ATP synthase

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