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Bioblasts - Richard Altmann and MiPArt by Odra Noel
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Molecular oxygen, O2 or dioxygen, has two atoms of oxygen, O, which is the chemical element with atomic number 8. The relative molecular mass of O2, Mr,O2, is 32 (or 31.9988). The element O has 8 protons, 8 neutrons and 8 electrons. In the figure, the two electrons in the first electron shell are not shown. Of the six electrons in the outer shell (blue bullets), one electron from each of the two atoms is shared in O2 forming the covalent bond, and one electron in each atom is unpaired.

Abbreviation: O2

Reference: Gnaiger 1983 POS symbols

Oxygen gas

At STP, molecular oxygen is a diatomic gas. The volume fraction of oxygen in dry clean air is constant at 0.20947 from sea level up to atmospheric altitude of 90 to 95 km. The partial pressure of oxygen, pO2, in air is a function of altitude and water vapor pressure.
The molar volume of an ideal gas at a pressure of 100 kPa (1 bar) and 0 °C is 22.711 L·mol-1 and at 1 atm (101.325 kPa) it is 22.414 L·mol-1. Under these conditions (STP), the real volume of O2 is 22.392 L·mol-1 [1].
More details: » Gas law, » Gas constant

Dissolved oxygen

Oxygen gas is soluble in water at an oxygen solubility, SO2, that depends on temperature and the concentration and type of dissolved substances.

Oxygen as respiratory substrate

Molecular oxygen is a substrate of cytochrome c oxidase (Complex IV) or alternative oxidases in aerobic cellular respiration. The product of the complete reduction is water, H2O, in the reaction catalyzed by cytochrome c oxidase. On the other hand, electron leak along the electron transfer-pathway in the presence of oxygen is a source of reactive oxygen species.

Keywords: Oxygen signal


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  1. Gnaiger E (1983) Calculation of energetic and biochemical equivalents of respiratory oxygen consumption. In: Polarographic Oxygen Sensors. Aquatic and Physiological Applications. Gnaiger E, Forstner H (eds), Springer, Berlin, Heidelberg, New York:337-45. - »Bioblast link«

MitoPedia topics: Substrate and metabolite