Question

The antibiotic piericidin, a nonpolar molecule, is structurally similar to ubiquinone (coenzyme \(\mathrm{Q}\) ) and can cross the mitochondrial membrane. What effect might the presence of piericidin have on oxidative phosphorylation?

Short answer

Piericidin inhibits electron transport, reducing ATP synthesis.

Step-by-step solution

Understand the Role of Coenzyme Q

Coenzyme Q (ubiquinone) is crucial in the electron transport chain within the mitochondria. It is involved in electron transfer by accepting electrons from Complex I and II and transferring them to Complex III, facilitating the proton gradient necessary for ATP synthesis.

Analyze Piericidin's Structural Similarity to Coenzyme Q

Given that piericidin is structurally similar to coenzyme Q, it can potentially interact with the same sites as coenzyme Q within the electron transport chain.

Evaluate Piericidin's Effect on Electron Transport

If piericidin binds to the locations meant for ubiquinone, it can inhibit the transfer of electrons between Complex I (or II) and Complex III. This interference would block the electron flow needed to maintain the proton gradient across the mitochondrial membrane.

Consider the Impact on Oxidative Phosphorylation

Oxidative phosphorylation depends on the proton gradient created through electron transport. If piericidin prevents electron transfer, the proton gradient will not form effectively, leading to reduced ATP production.

Key concepts

Electron Transport Chain

The electron transport chain (ETC) is a series of protein complexes embedded in the inner membrane of the mitochondria. It plays a vital role in cellular respiration by transferring electrons from electron donors like NADH and FADH2 to oxygen, which is the final electron acceptor. The ETC consists of four main complexes: Complex I (NADH dehydrogenase), Complex II (succinate dehydrogenase), Complex III (cytochrome b-c1 complex), and Complex IV (cytochrome c oxidase).

• Electrons move through these complexes, releasing energy at each step.
• The energy is used to pump protons (H⁺) from the mitochondrial matrix into the intermembrane space.
• This creates a proton gradient, known as the proton motive force.

The proton gradient is essential as it drives the synthesis of ATP—energy required for various cellular processes.

Mitochondria

Mitochondria are known as the powerhouse of the cell. These organelles are responsible for producing most of the cell's supply of ATP through oxidative phosphorylation. Mitochondria have a unique double membrane structure that is critical for their function:

• The outer membrane is permeable to small molecules and ions.
• The inner membrane is less permeable and contains the components of the electron transport chain and ATP synthase.

Inside the inner membrane is the mitochondrial matrix, a gel-like fluid containing enzymes for the Krebs cycle. This cycle generates the electron carriers, NADH and FADH2, which provide electrons to the electron transport chain.
The organization of mitochondria allows them to efficiently produce ATP and manage energy resources within a cell.

ATP Synthesis

ATP synthesis is the process of producing adenosine triphosphate (ATP), the energy currency of the cell. This process primarily occurs in mitochondria during oxidative phosphorylation. The energy required for ATP synthesis is obtained from the proton gradient produced by the electron transport chain. In the inner mitochondrial membrane, ATP synthase is the key enzyme that facilitates ATP production. It uses the proton motive force generated by the proton gradient as protons flow back into the mitochondrial matrix. This movement of protons provides the energy needed for ATP synthase to convert adenosine diphosphate (ADP) and inorganic phosphate (Pi) into ATP.

• ATP is used by cells to perform various functions, such as muscle contraction and active transport of molecules across cellular membranes.
• Efficient ATP synthesis is crucial for cellular vitality and energy conservation.

Coenzyme Q

Coenzyme Q, also known as ubiquinone, is a lipid-soluble molecule found within the electron transport chain. It functions as an electron carrier:

• It receives electrons from Complexes I and II.
• It transfers these electrons to Complex III, facilitating the continuation of electron flow through the chain.

Coenzyme Q is crucial for maintaining efficient electron transport, which is needed to sustain the proton gradient essential for ATP synthesis.
Given its role, any interference with coenzyme Q can disrupt the electron flow and negatively impact ATP production.
For example, if an inhibitor like piericidin binds at coenzyme Q's site, electron transfer could be blocked, leading to decreased ATP availability. Therefore, coenzyme Q's function is indispensable in the overall process of cellular energy production.