Chapter 4 - Redox reactions and ATP synthesis in the cell

Abstract

Ligands are hormones, neurotransmitters, second messengers, or substrates of an enzyme. Binding between a ligand and its receptor results from intermolecular forces and changes the three-dimensional shape of the target protein. The target protein may be enzymes, ligand-gated ion channels, or G protein-coupled transmembrane proteins. The binding occurs over an infinitesimal range of time, and it is reversible. Redox reactions are characterized by the shift of electrons from the reducing agent to the oxidizing agent at higher electric potential. Oxygen atom attracts electrons strongly toward itself, and two electrons from NADH tends to be pulled by the oxidoreductases in the complex I, III, and oxidase in the complex IV, releasing protons into the intermembrane space through the complexes, but not be pulled toward NAD+, and the negatively charged oxygen atom after accepting two electrons combines with two protons from the matrix, to produce water by cytochrome c oxidase. The electrochemical potential of the protons produced through a series of electron transport in mitochondria drives two molecular motors of F0F1 ATP-synthase. Without sufficient oxygen, the electron transfer stops, and ATP synthesis comes to a halt when the electrochemical potential of the proton diminishes, and then the enzyme works in the reverse direction as a proton pump using bonding energy from ATP hydrolysis.