When electrons flow along the electron transport chains of mitochondria, which of the following changes occurs?a. The pH of the matrix increases.b. ATP synthase pumps protons by active transport.c. The electrons gain free energy.d. NAD+ is oxidized.

Verified step by step guidance

1. Identify the role of the electron transport chain (ETC) in mitochondria, which is to transfer electrons from electron donors to electron acceptors via redox reactions.
2. Understand that as electrons move through the ETC, they release energy, which is used to pump protons (H+) from the mitochondrial matrix to the intermembrane space, creating a proton gradient.
3. Recognize that the movement of protons into the intermembrane space decreases the pH there, while the pH of the matrix increases as protons are pumped out.
4. Recall that ATP synthase uses the proton gradient to synthesize ATP from ADP and inorganic phosphate, but it does not pump protons by active transport; instead, it allows protons to flow back into the matrix, driving ATP synthesis.
5. Note that NAD+ is reduced to NADH during earlier stages of cellular respiration, and in the ETC, NADH is oxidized back to NAD+ as it donates electrons.

Key Concepts

Electron Transport Chain (ETC)

The electron transport chain is a series of protein complexes located in the inner mitochondrial membrane that facilitate the transfer of electrons from electron donors like NADH and FADH2 to electron acceptors. This process generates a proton gradient across the membrane, which is essential for ATP production through oxidative phosphorylation.

Proton Gradient and pH Changes

As electrons move through the ETC, protons (H+) are pumped from the mitochondrial matrix into the intermembrane space, creating a proton gradient. This gradient leads to a decrease in pH in the intermembrane space and an increase in pH in the matrix, which is crucial for ATP synthesis as protons flow back into the matrix through ATP synthase.

ATP Synthase Function

ATP synthase is an enzyme that synthesizes ATP from ADP and inorganic phosphate, utilizing the energy from the proton gradient established by the ETC. It operates through a process called chemiosmosis, where protons flow down their concentration gradient through ATP synthase, driving the conversion of ADP to ATP.