Bio 2

Electron Transport Chain Overview

• The electron transport chain (ETC) occurs in the mitochondrial membrane and plays a crucial role in ATP production.

• Each glucose molecule can yield up to 34 ATP through this process.

• Compared to glycolysis, this is 17 times more efficient.

Role of NADH and FADH2

• NADH and FADH2 are crucial electron carriers in cellular respiration.

• NADH is produced from the reduction of NAD+; it carries high-energy electrons to the ETC.

• FADH2, another electron donor, contributes to the chain but at a lower energy state than NADH.

Mitochondrial Functionality

Mitochondria:

• Are double-membraned organelles responsible for energy production.

• The inner membrane creates a barrier for protons, establishing a proton gradient vital for ATP synthesis.

ATP Synthase:

• The protein complex ATP synthase uses the proton gradient to synthesize ATP.

• The flow of protons spins ATP synthase to create energy, much like a turbine.

• Without a proton gradient, ATP production halts, leading to energy depletion in the cell.

The Process of Pyruvate Conversion

• Glycolysis occurs in the cytoplasm, producing two pyruvate molecules from glucose.

• Pyruvate is transported into the mitochondrial matrix via a carrier protein.

• Inside the matrix, pyruvate is converted into acetyl CoA by pyruvate dehydrogenase, generating CO2 and reducing NAD+ to NADH.

The Citric Acid Cycle (Kreb's Cycle)

• Links glycolysis to the electron transport chain.

• Comprises eight steps; starts with acetyl CoA combining with oxaloacetate to form citrate.

• Produces three NADH and one FADH2 per cycle, harvesting energy.

The Electron Transport Chain Components

Protein Complexes:

• Four main protein complexes exist (I-IV) in the inner mitochondrial membrane.

• Complexes I, III, and IV pump protons (H+) from the matrix to the intermembrane space.

• Complex II promotes proton pumping but does not pump protons directly.

Complex-specific Functions

Complex I:

• Receives high-energy electrons from NADH.

• Electrons are passed along redox centers, releasing energy that pumps protons into the intermembrane space.

• Delivers electrons to coenzyme Q (ubiquinone).

Complex II:

• Accepts electrons from FADH2 and transfers them via redox centers to coenzyme Q.

• Does not pump protons into the intermembrane space.

Complex III and IV:

• Coenzyme Q donates electrons to Complex III, where a recyclable electron re-enters.

• Electrons travel to cytochrome c, which then carries them to Complex IV.

• Complex IV converts oxygen (O2) to water (H2O) and pumps additional protons, strengthening the gradient.

Oxygen's Role: Final Electron Acceptor

• Oxygen is essential as it serves as the final electron acceptor in the ETC.

• In the absence of oxygen, the electron transfer ceases, halting ATP production, emphasizing the necessity of respiration.

Summary of Energy Production

• The inner mitochondrial membrane is densely packed with these complexes, functioning as a giant power plant.

• Efficient ATP production is reliant on the intricate enzyme systems and proton gradients positioned within the mitochondria.

• A common misconception: Photosynthesis involves light splitting water; this is inaccurate.