What Happens To The Concentration Of H+ In The Intermembrane Space And The Matrix As Electrons Move Down The ETC?
The correct answer and explanation is :
As electrons move down the electron transport chain (ETC), the concentration of hydrogen ions (H⁺) in the intermembrane space of the mitochondrion increases, while the concentration of H⁺ in the matrix decreases.
Here’s an explanation of the process:
- Electron Transport Chain Overview: The ETC is located in the inner mitochondrial membrane, where a series of protein complexes (Complexes I, II, III, and IV) facilitate the transfer of electrons from high-energy molecules, like NADH and FADH₂, to molecular oxygen (O₂), which is reduced to form water (H₂O). This process is integral to cellular respiration, where the main goal is to generate a proton gradient that will be used to produce ATP.
- Proton Pumping: As electrons move through the ETC, energy is released. This energy is used by certain complexes, such as Complexes I, III, and IV, to actively pump protons (H⁺) from the mitochondrial matrix into the intermembrane space. As a result, the intermembrane space becomes highly enriched with H⁺, creating an electrochemical gradient (also known as a proton gradient) across the inner mitochondrial membrane.
- Effect on the Matrix: As protons are pumped out into the intermembrane space, the concentration of H⁺ in the matrix decreases. This decrease in proton concentration in the matrix contributes to the formation of a negative charge relative to the intermembrane space.
- Chemiosmosis and ATP Synthesis: The proton gradient generated by the ETC creates a potential energy difference, known as the proton motive force (PMF). This force drives protons back into the matrix through ATP synthase. As protons flow through ATP synthase, the energy released is used to synthesize ATP from ADP and inorganic phosphate (Pi).
In summary, the movement of electrons down the ETC leads to the active pumping of H⁺ into the intermembrane space, resulting in a higher concentration of protons there and a lower concentration in the matrix. This creates the proton gradient necessary for ATP production through chemiosmosis.