B2.2.4 Adaptations of the mitochondrion for production of ATP by aerobic cell respiration (HL) Notes

Mitochondrial Adaptations Optimize ATP Production in Aerobic Respiration

1. The mitochondrion is enclosed by an outer membrane and a highly folded inner membrane, creating distinct compartments for different stages of aerobic respiration.
2. This separation allows specific biochemical processes (e.g., Krebs cycle in the matrix, oxidative phosphorylation on the inner membrane) to occur in optimal conditions.

The Outer Membrane Is A Controlled Gateway

1. It is selectively permeable, allowing small molecules like pyruvate and oxygen to enter while excluding larger, potentially disruptive molecules.
2. This regulation helps maintain a suitable environment for the complex reactions inside the mitochondrion.

The Intermembrane Space Is A Proton Reservoir

1. Protons (H⁺) are pumped into this narrow space during the electron transport chain (ETC), creating a steep concentration gradient.
2. The small volume of this space ensures that even a modest influx of protons quickly raises the proton concentration, crucial for ATP synthesis.

The Inner Membrane Is The Site of ATP Production

1. This membrane hosts the ETC and ATP synthase, the key proteins in oxidative phosphorylation.
2. Its folded structure (forming cristae) significantly increases surface area, maximizing the number of ETC proteins and boosting ATP output.

Cristae Maximizes Surface Area

1. Cristae are folds in the inner membrane that dramatically expand its surface.
2. More surface area allows more ETC and ATP synthase complexes to be embedded, leading to greater ATP production.

Embedded Proteins Fuel ATP Production

1. The electron transport chain passes electrons and pumps protons into the intermembrane space, setting up the proton gradient.
2. ATP synthase harnesses this gradient to convert ADP and inorganic phosphate into ATP, the cell’s primary energy currency.

The Matrix Is The Hub of the Krebs Cycle

1. The matrix contains enzymes and substrates for the Krebs cycle and the link reaction, generating NADH and FADH₂.
2. These electron carriers fuel the ETC, driving further ATP production.
3. The matrix also holds mitochondrial DNA and 70S ribosomes, enabling the mitochondrion to synthesize some of its own proteins quickly.

Mitochondrial DNA and Ribosomes

1. The matrix also contains mitochondrial DNA and 70S ribosomes, enabling the mitochondrion to produce some of its own proteins.
   1. This autonomy allows the mitochondrion to quickly synthesize proteins essential for its energy-generating functions.

How the Adaptations Work Together

1. Compartmentalization (outer membrane, intermembrane space, and matrix) streamlines each step of aerobic respiration.
2. Cristae provide a vast surface for more ETC components and ATP synthase.
3. The steep proton gradient in the intermembrane space efficiently powers ATP synthesis.
4. The matrix concentrates the enzymes and substrates of the Krebs cycle, speeding up reactions and ensuring a steady supply of electron carriers.

Applications and Broader Implications

1. Mitochondrial dysfunction is linked to neurodegenerative diseases (e.g., Parkinson’s), highlighting the importance of efficient ATP production.
2. Athletic performance is partly determined by mitochondrial efficiency, which affects muscle energy availability.