Electron Transport Chain: ATP Synthesis & Oxygen's Role

The Electron Transport Chain: ATP Production

Inside the inner membrane of the mitochondria, there is a chain of electron carriers known as the electron transport chain (ETC). Electrons generated from oxidative reactions in earlier stages of cellular respiration pass along this chain.

NADH donates two electrons to the first carrier. As these electrons pass along the chain, they release energy from one carrier to the next. At three specific locations along the chain, sufficient energy is released to synthesize ATP via ATP synthase, an enzyme also located in the inner mitochondrial membrane.

FADH₂ also donates electrons, but at a later stage than NADH. Electrons from FADH₂ release enough energy at only two locations along the chain. This ATP production, relying on energy release through oxidation, is therefore termed oxidative phosphorylation.

Oxygen's Crucial Role in Cellular Respiration

Oxygen is crucial for cellular respiration because, at the end of the electron transport chain, electrons are donated to it. This process occurs in the mitochondrial matrix, at the surface of the inner membrane. Simultaneously, oxygen binds with hydrogen ions to form water.

Without oxygen, electrons can no longer pass through the electron transport chain. Consequently, NADH + H⁺ cannot be reconverted into NAD⁺. Eventually, the supply of NAD⁺ in the mitochondrion depletes, halting both the link reaction and the Krebs cycle.

Key Mitochondrial Structures and Functions

Matrix

A watery substance containing ribosomes and numerous enzymes crucial for the link reaction and the Krebs cycle.

Inner Membrane

Houses the electron transport chain and ATP synthase, both essential for oxidative phosphorylation.

Space Between Inner and Outer Membranes

A small volume space where protons are pumped, allowing a high concentration gradient to be quickly achieved, vital for chemiosmosis.

Outer Membrane

Separates the mitochondrion's contents from the rest of the cell, creating an optimal environment for cellular respiration.

Cristae

Tubular projections of the inner membrane that significantly increase the surface area available for oxidative phosphorylation.