Question

As per chemiosmotic coupling hypothesis, in protons accumulate in the (a) outer membrane (b) inner membrane (c) intermembrane space (d) matrix.

Short answer

Protons accumulate in the (c) intermembrane space according to the chemiosmotic coupling hypothesis.

Step-by-step solution

Understanding the Chemiosmotic Coupling Hypothesis

The chemiosmotic coupling hypothesis, proposed by Peter Mitchell, describes how ATP is generated in the mitochondria. When electrons are transported through the electron transport chain, protons are pumped from the mitochondrial matrix to the intermembrane space, creating a proton gradient.

Identifying where Protons Accumulate

According to the hypothesis, the protons are pumped out of the matrix and accumulate in the intermembrane space. This creates a proton motive force which is used by the enzyme ATP synthase to produce ATP as protons flow back into the matrix.

Selecting the Correct Option

Given the area where protons accumulate as described in the hypothesis, the correct answer where protons accumulate is the intermembrane space.

Key concepts

ATP Synthesis

Adenosine triphosphate (ATP) synthesis is the fundamental process by which cells generate energy. In the mitochondria, this process is highly dependent on a flow of protons.

This flow is catalyzed by the enzyme ATP synthase, which operates like a tiny molecular turbine. As protons move through ATP synthase, they rotate parts of the molecule, providing the energy required to convert adenosine diphosphate (ADP) and inorganic phosphate (Pi) into ATP.

Key to Energy Production

The synthesis of ATP in this manner is vital for numerous cellular processes, as it provides the primary energy currency that powers most biochemical reactions within the cell.

Electron Transport Chain

The electron transport chain is a series of protein complexes and small molecules that facilitate the transfer of electrons from donors to acceptors via redox reactions, coupled with the transfer of protons (H+ ions) across a membrane.

This chain is embedded in the inner mitochondrial membrane. As electrons are passed along the chain from one carrier protein to another, the energy released from these electrons is used to pump protons from the mitochondrial matrix across the inner membrane into the intermembrane space, creating the vital proton gradient necessary for ATP synthesis.

Efficiency and Control

The electron transport chain is highly efficient and is regulated to meet the energy demands of the cell, providing an elegant system of energy conversion.

Proton Motive Force

Proton motive force (PMF) is the force generated by the build-up of a gradient of protons across a membrane which is directly used to drive ATP synthesis.

Essentially, it is the stored energy of this gradient, analogous to water pressure behind a dam, which has the potential to do work. In mitochondria, this force is created by the movement of protons into the intermembrane space during electron transport. The PMF consists of two components: a difference in proton concentration (a chemical gradient) and a difference in charge (an electrical gradient) across the membrane.

Driving Cellular Work

The proton motive force is what ultimately powers the ATP synthase to synthesize ATP, providing a key linkage between the electron transport chain and ATP production.

Mitochondrial Matrix

The mitochondrial matrix is the innermost compartment of the mitochondria, enclosed by the inner membrane. It contains enzymes that are responsible for the citric acid cycle (also known as the Krebs cycle), along with DNA, ribosomes, and other molecules essential for mitochondrial function.

It is in the matrix that the protons originate before being pumped across the inner mitochondrial membrane. The return flow of these protons from the intermembrane space to the matrix is what drives ATP synthesis.

A Hub of Metabolic Activity

The mitochondrial matrix plays a pivotal role in energy production and metabolic pathways of the cell, making it essential for life.

Intermembrane Space

The intermembrane space is the region between the inner and outer membranes of the mitochondria. This space becomes crucially important in energy production as it serves as a reservoir for the protons pumped from the matrix by the electron transport chain.

The accumulation of protons here contributes to the generation of the proton motive force. Once the gradient is established, it can be used by ATP synthase, which spans the inner membrane, to manufacture ATP as protons rush back into the matrix following their electrochemical gradient.

Vital for ATP Production

The intermembrane space is not just an empty void; it's a critical player in the overall process of ATP synthesis, demonstrating the importance of compartmentalization in cellular biology.