Question

In the electron transport system present in the inner mitochondrial membrane, complexes I and IV are respectively (a) NADH dehydrogenase and \(\mathrm{FADH}_{2}\) (b) \(\mathrm{FADH}_{2}\) and NADH dehydrogenase (c) NADH dehydrogenase and cytochrome oxidase complex (d) NADH dehydrogenase and ATP synthase.

Short answer

The correct answers for Complexes I and IV are respectively (c) NADH dehydrogenase and cytochrome oxidase complex.

Step-by-step solution

Understanding the Electron Transport Chain

The Electron Transport Chain (ETC) is a series of protein complexes that transfer electrons through a membrane within mitochondria to create a gradient of protons that drives the production of ATP. Complex I is the first protein complex in the ETC, while Complex IV is the final one.

Identifying Complex I

Complex I of the electron transport chain is known as NADH dehydrogenase. It receives electrons from NADH and transfers them to ubiquinone (coenzyme Q), which is not part of the answer choices directly but helps to identify complex I as NADH dehydrogenase.

Identifying Complex IV

Complex IV is known as cytochrome c oxidase or cytochrome oxidase complex. It receives electrons from cytochrome c and uses these electrons to reduce oxygen to water.

Choose the Correct Answer

From the options provided, select the choice that correctly names Complex I as NADH dehydrogenase and Complex IV as cytochrome oxidase complex.

Key concepts

NADH dehydrogenase

NADH dehydrogenase, also known as Complex I, plays a pivotal role in the electron transport chain (ETC), which is essential for cellular respiration in eukaryotic organisms. This large protein complex is embedded in the inner mitochondrial membrane and kicks off the ETC by accepting electrons from the molecule NADH. As it transfers these electrons to ubiquinone (coenzyme Q), it pumps protons from the mitochondrial matrix into the intermembrane space.

Understanding NADH dehydrogenase is crucial because it initiates the proton gradient that ultimately powers ATP synthesis. Any disruption to the function of this complex can have significant effects on ATP generation and an organism's overall energy balance.

cytochrome oxidase complex

The cytochrome oxidase complex, or Complex IV of the ETC, is another vital component located in the inner mitochondrial membrane. This complex receives electrons from cytochrome c, which have been passed along a chain of previous complexes and carriers. With these electrons, Complex IV catalyzes the reduction of oxygen to water—a vital step, as oxygen is the final electron acceptor in the chain.

The process of reducing oxygen also contributes to the proton gradient by pumping more protons across the membrane. This process of electron transfer and coupling with oxygen is what links the electron transport chain to the essential metabolic process of aerobic respiration.

mitochondrial membrane

The inner mitochondrial membrane plays a central role in energy production within a cell. This membrane is impermeable to most ions and molecules, a property that is crucial for its function. As electron carriers and protein complexes like NADH dehydrogenase and cytochrome oxidase complex perform their actions, they create a difference in proton concentration across this membrane.

The potential energy from this proton gradient, also known as the proton motive force, is what drives the synthesis of ATP, the cell's energy currency. The mitochondrial membrane's integrity and its ability to maintain this gradient are therefore essential for efficient ATP production and overall cellular health.

ATP production

ATP production, or ATP synthesis, is the final and most important outcome of the electron transport chain. ATP, or adenosine triphosphate, serves as the primary energy currency of the cell. The process of ATP production is driven by a proton gradient across the inner mitochondrial membrane, established by the activity of electron transport complexes.

The enzyme ATP synthase, which is also embedded in the inner mitochondrial membrane, harnesses the energy of the flowing protons back into the matrix to synthesize ATP from ADP and inorganic phosphate. This process is known as oxidative phosphorylation, as it links the phosphorylation of ADP with the oxidation of the carriers in the electron transport chain.