Function of Oxygen

If the last cytochrome remained in a reduced state, it would be unable to accept more electrons. Electron transport would then progress only to the next-to-last cytochrome. This process would continue until all of the elements of the electron-transport chain remained in the reduced state. At this point, the electron-transport system would stop functioning and no ATP could be produced in the mitochondria. With the electron-transport system incapacitated, NADH and FADH2 could not become oxidized by donating their electrons to the chain and, through inhibition of Krebs cycle enzymes, no more NADH and FADH2 could be produced in the mitochondria. The Krebs cycle would stop and respiration would become anaerobic.

Krebscyclus Mitochondria

■ Figure 5.10 A schematic representation of the chemiosmotic theory. The matrix and the compartment between the inner and outer mitochondrial membranes showing how the electron-transport system functions to pump H+ from the matrix to the intermembrane space. This results in a steep H+ gradient between the intermembrane space and the cytoplasm of the cell. The diffusion of H+ through ATP synthase results in the production of ATP.

■ Figure 5.10 A schematic representation of the chemiosmotic theory. The matrix and the compartment between the inner and outer mitochondrial membranes showing how the electron-transport system functions to pump H+ from the matrix to the intermembrane space. This results in a steep H+ gradient between the intermembrane space and the cytoplasm of the cell. The diffusion of H+ through ATP synthase results in the production of ATP.

Cell Respiration and Metabolism

Oxygen, from the air we breathe, allows electron transport to continue by functioning as the final electron acceptor of the electron-transport chain. This oxidizes cytochrome a3, allowing electron transport and oxidative phosphorylation to continue. At the very last step of aerobic respiration, therefore, oxygen becomes reduced by the two electrons that were passed to the chain from NADH and FADH2. This reduced oxygen binds two protons, and a molecule of water is formed. Since the oxygen atom is part of a molecule of oxygen gas (O2), this last reaction can be shown as follows:

Cyanide is a fast-acting lethal poison that produces such symptoms as rapid heart rate, tiredness, seizures, and headache. Cyanide poisoning can result in coma, and ultimately death, in the absence of quick treatment. The reason that cyanide is so deadly is that it has one very specific action: it blocks the transfer of electrons from cytochrome a3 to oxygen. The effects are thus the same as would occur if oxygen were completely removed—aerobic cell respiration and the production of ATP by oxidative phosphorylation comes to a halt.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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