Question

Electron-transfer reactions occur rapidly. Which of the following statements best describes how the diffusion of ubiquinone is controlled in order to ensure its proximity to the other enzyme complexes?

(a) Ubiquinone is anchored directly in the inner mitochondrial membrane via its hydrocarbon tail, and can only diffuse laterally.
(b) Ubiquinone is present at high concentrations, minimizing the impact of diffusion on the electron-transport chain.
(c) Ubiquinone becomes covalently attached to the other enzyme complexes.
(d) The intermembrane space in the mitochondrion is relatively small, and therefore the random diffusion of these molecules is not a problem.

Answer 1

Ubiquinone is anchored in the mitochondrial membrane, allowing only lateral diffusion, which efficiently facilitates electron transfer between complexes in the electron transport chain.

Step-by-step explanation:

The best description of how the diffusion of ubiquinone is controlled to ensure its proximity to other enzyme complexes is (a) Ubiquinone is anchored directly in the inner mitochondrial membrane via its hydrocarbon tail, and can only diffuse laterally. Ubiquinone, also known as coenzyme Q, is a small, lipid-soluble molecule that plays a critical role in the electron transport chain (ETC) of cellular respiration, a biochemical process that occurs in the inner mitochondrial membrane and generates ATP.

Ubiquinone receives electrons from both complex I, which handles electrons from NADH, and complex II, which accepts electrons from FADH2. As a mobile electron carrier, ubiquinone moves within the hydrophobic core of the mitochondrial membrane, ensuring its actions are limited to a two-dimensional space.

This constrained lateral diffusion facilitates efficient electron transfer between the enzyme complexes. Ubiquinone's role is vital, as it shuttles electrons to complex III, which continues the process of building a proton gradient essential for ATP synthesis.