Question

ETS is present in (a) Stroma (b) Matrix of mitochondria (c) Inner membrane of mitochondria (d) Outer membrane of mitochondria

Short answer

ETS is located in the inner membrane of mitochondria.

Step-by-step solution

Identify location of ETS

The ETS is composed of four protein complexes: Complex I, II, III and IV. Each protein complex is located in the inner mitochondrial membrane. The complexes drive the electrons from donors to acceptors through redox reactions, and the transfer of electrons is coupled with the transport of protons aka hydrogen ions (H+) across the inner mitochondrial membrane. Thus, ETS is located in Inner membrane of mitochondria.

Choose the correct option

Based on the identification of the location of ETS in Step 1, the correct option would be the inner membrane of mitochondria.

Key concepts

Mitochondria

The mitochondria, often referred to as the 'powerhouse of the cell', play a crucial role in cellular energetics. Within these organelles, a complex process named cellular respiration converts nutrients into ATP, the energy currency of the cell, which powers most cellular functions. Structurally, mitochondria have an outer membrane that encases the entire structure, an intermembrane space between the outer and inner membranes, and a convoluted inner membrane that contains folds called cristae to increase surface area.

These cristae are the location of the electron transport system (ETS), which is essential for the production of ATP. Moreover, the matrix enclosed by the inner membrane contains enzymes that carry out reactions responsible for generating electron carriers used in the ETS. The exquisite architecture of the mitochondria is integral to their function, ensuring that the processes of energy production are as efficient as possible.

Redox Reactions

Redox reactions are chemical processes that involve the transfer of electrons between two substances. They consist of two half-reactions: oxidation, where an electron is lost, and reduction, where an electron is gained. These reactions are a fundamental aspect of the ETS involving the transfer of electrons from electron donors to acceptors through a series of protein complexes.

During this series of electron transfers, energy is released which is harnessed by the protein complexes to pump protons across the inner mitochondrial membrane, creating an electrochemical gradient. The culmination of this gradient results in the production of ATP, as the flow of protons back into the mitochondrial matrix through ATP synthase drives the synthesis of ATP from ADP and inorganic phosphate. Without redox reactions, the process of oxidative phosphorylation, which generates the majority of ATP in aerobic organisms, would not be possible.

Protein Complexes in Mitochondria

The inner membrane of mitochondria houses a series of protein complexes, each playing a unique role in the ETS. These complexes, labeled I through IV, are embedded within the membrane and work in concert to transport electrons—received from carriers such as NADH and FADH₂—down the electron transport chain.

Complex I, also known as NADH: ubiquinone oxidoreductase, initiates the process by transferring electrons from NADH to ubiquinone. Complex II, which also contributes to this transfer, receives electrons from FADH₂. Complex III, or cytochrome b-c1 complex, then moves the electrons to cytochrome c, while pumping protons across the membrane. Complex IV, also called cytochrome c oxidase, completes the transfer by moving electrons to oxygen, the final electron acceptor, forming water. This orchestrated flow of electrons, coupled with the translocation of protons across the inner membrane, facilitates the generation of ATP.