Question

When oxidative phosphorylation is uncoupled, does oxygen consumption decrease, increase, or stay the same? Explain.

Short answer

Oxygen consumption increases when oxidative phosphorylation is uncoupled.

Step-by-step solution

Understanding Oxidative Phosphorylation

Oxidative phosphorylation is a metabolic pathway using energy released by the oxidation of nutrients to produce ATP. It occurs in mitochondria and involves the electron transport chain and chemiosmosis, using oxygen as the final electron acceptor.

Role of Proton Gradient

Typically, electron transport via the electron transport chain pumps protons across the mitochondrial membrane, creating a proton gradient. This gradient is crucial for ATP synthase to produce ATP.

Effect of Uncoupling

Uncoupling disrupts the proton gradient by allowing protons to flow back across the membrane without passing through ATP synthase. This means the energy of the gradient is released as heat rather than being used to produce ATP.

Impact on Oxygen Consumption

Because electron transport can continue independently of ATP synthesis when uncoupling occurs, oxygen consumption does not decrease. In fact, it may increase since electron transport continues without the regulatory feedback from ATP synthesis.

Key concepts

Electron Transport Chain

The Electron Transport Chain is a series of complexes found within the inner membrane of mitochondria. It plays a crucial role in the process of oxidative phosphorylation. Electrons are transferred through a series of protein complexes and molecules, namely Complex I to IV, which are embedded in the mitochondrial membrane.
This chain of electron carriers passes electrons derived from NADH and FADH₂ to oxygen, the final electron acceptor. As electrons flow through these complexes, energy is released, which is used to pump protons from the mitochondrial matrix into the intermembrane space, creating an electrochemical gradient.
The Electron Transport Chain is essential for cellular respiration and energy production, as it is the first step in setting up the conditions needed for ATP synthesis.

ATP Synthesis

ATP Synthesis is the process by which ATP, the energy currency of the cell, is produced. It occurs in the mitochondria, specifically at the enzyme complex known as ATP synthase. This remarkable enzyme harnesses the energy from the proton gradient established by the electron transport chain.
As protons flow back into the mitochondrial matrix through ATP synthase, driven by the gradient, the enzyme rotates. This mechanical movement facilitates the phosphorylation of ADP, converting it into ATP.
This process, known as chemiosmosis, is fundamental to energy production in aerobic organisms and can be thought of as a biological turbine generating ATP through the flow of protons.

Proton Gradient

The Proton Gradient is the concentration difference established by the active transport of protons across the inner mitochondrial membrane during electron transport. This difference not only creates a chemical gradient (pH difference) but also an electrical gradient across the membrane.
The gradient is a form of potential energy commonly referred to as the proton-motive force. This force is indispensable for ATP synthesis as it drives the protons back into the mitochondrial matrix through ATP synthase, facilitating the conversion of ADP to ATP.
Maintaining this gradient is essential for efficient energy production, and any disruption, like uncoupling, can divert the energy to generate heat instead of ATP.

Mitochondria

Mitochondria are often called the powerhouses of the cell and are the organelles where oxidative phosphorylation takes place. They are enveloped by two membranes, providing compartments critical for their function in energy production.
The inner membrane forms cristae, which greatly increase the surface area available for the electron transport chain and ATP synthesis. Inside, the mitochondrial matrix hosts the citric acid cycle, supplying electron carriers like NADH and FADH₂ to the electron transport chain.
Mitochondria are unique due to their own DNA and ability to produce a portion of their required proteins independently. Their ability to efficiently produce ATP makes them vital for high-energy demanding processes in cells.