Lesson 8: Cellular Respiration - Oxidative Phosphorylation

the electron transport chain (ETC) and chemiosmosis

Oxidative phosphorylation has two parts:

Electron Transport Chain

is a collection of proteins bound to the inner mitochondrial membrane and organic molecules, which electrons pass through in a series of redox reactions, and release energy. The energy released forms a proton gradient, which is used in chemiosmosis to make a large amount of ATP by the protein ATP-synthase.

atmospheric oxygen

The electron transport chain is the last component of aerobic respiration and is the only part of glucose metabolism that uses ?

Complex I

oxidizes NADH, transferring electrons to coenzyme Q while pumping protons into the intermembrane space.

ubiquinone oxidoreductase

Complex I is also known as

Complex II

transfers electrons from FADH₂ to coenzyme Q without contributing to proton pumping.

succinate dehydrogenase

Complex II other name

Coenzyme Q

also known as ubiquinone (CoQ), is made up of quinone and a hydrophobic tail. Its purpose is to function as an electron carrier and transfer electrons to complex III.

cytochrome c reductase

Complex III other name

Complex III

transfers electrons from ubiquinol to cytochrome c, using the Q-cycle to pump protons.

cytochrome c oxidase

Complex IV other name

Complex IV

transfers electrons from cytochrome c to oxygen, forming water and pumping protons into the intermembrane space.

Complex V

uses the proton gradient to synthesize ATP as protons flow back into the mitochondrial matrix.

ATP Synthase

Complex V other name

Chemiosmosis

the free energy from the series of redox reactions just described, is used to pump hydrogen ions (protons) across the membrane. The uneven distribution of H+ ions across the inner mitochondrial membrane establishes both concentration and electrical gradients (thus, an electrochemical gradient), owing to the hydrogen ions’ positive charge and their aggregation on one side of the membrane. If the membrane were open to diffusion by the hydrogen ions, the ions would tend to diffuse back across into the intermembrane, driven.

Chemiosmosis

is used to generate 90% of the ATP made during aerobic glucose catabolism; it is also the method used in the light reactions of photosynthesis to harness the energy of sunlight in the process of photo- phosphorylation.