A Year of (Bio)chemical Elements

Breathe deep — for August, it’s oxygen

Quira Zeidan
August 01, 2019

We mark the 150th anniversary of Dimitri Mendeleev’s periodic table of chemical elements this year by highlighting elements important for life. So far, we’ve covered hydrogen, iron, sodium, potassium, chlorine, copper, calcium, phosphorus, carbon and nitrogen.

Oxygen Photosynthetic organisms capture the energy of sunlight and use it to produce organic molecules from the carbon dioxide and water they obtain from the environment. In the process, oxygen is released to the atmosphere.

For August, we selected oxygen, a highly reactive nonmetal with chemical symbol O and atomic number 8. Oxygen tends to fill its two unpaired electron shells by accepting electrons from other atoms via covalent bonding. It forms oxide compounds with a variety of elements, and its most common oxidation state is -2, but it also can exist in oxidation states of -1, +1 and +2.

After hydrogen and helium, oxygen is the third most abundant chemical element in the known universe. It is the second most abundant element in the Earth’s geosphere after iron and the most abundant element by mass in the Earth’s crust — at about 47% to 49%. Oxygen makes up about 89% of the world’s oceans, and diatomic oxygen gas constitutes about 20% of the Earth’s atmosphere — second only to nitrogen.

Oxygen is an important contributor to the evolution of all life on Earth. The earliest cells used components of the early Earth’s atmosphere — CO, CO2, N2 and CH4 — to synthesize organic compounds with the help of volcanic heat and lightning. Cells gradually developed pigments that capture visible light from the sun, acquired the ability to use H2O as the electron donor in photosynthetic reactions and started to eliminate O2 as waste. Under these conditions, the earth’s atmosphere grew richer in oxygen.

Aerobic organisms that live in habitats with a plentiful supply of O2 transfer electrons from fuel molecules to oxygen, deriving energy for preservation and growth. Their anaerobic counterparts have evolved in environments devoid of oxygen and transfer their electrons to nitrate, sulfate or carbon dioxide, forming dinitrogen, hydrogen sulfide and methane, respectively.

Aerobe cells obtain molecular oxygen from the surrounding medium by diffusion through their plasma membrane. However, oxygen is poorly soluble in the cytoplasm and extracellular milieu, and it cannot be diffused over long distances. Organisms have evolved water-soluble proteins that use transition metals such as iron and copper to store and transport oxygen in aqueous environments. Proteins such as hemoglobin and myoglobin use iron in the prosthetic group heme to bind oxygen reversibly and move it through tissues.

Cytochromes also use heme to transfer electrons in oxidation-reduction reactions during cellular respiration and photosynthesis. The constant movement of electrons inside the cell generates reactive oxygen species as byproducts, mostly superoxide ions and hydrogen peroxide. The immune cells of some vertebrates and certain plants use these reactive species to destroy invading microorganisms and pathogens.

Oxygen is a major constituent of the biological molecules in living beings. Chemical groups that contain oxygen include the hydroxyls, carbonyls and carboxyls in alcohols plus aldehydes, ketones, carboxylic acids and esters. These organic compounds are the building blocks for proteins, nucleic acids, carbohydrates and fats, the structural components of cells and tissues. Oxygen is also an important constituent of inorganic compounds important for life, such as water and phosphate.

Quira Zeidan

Quira Zeidan is the ASBMB’s education and public outreach coordinator.

Join the ASBMB Today mailing list

Sign up to get updates on articles, interviews and events.

Latest in Science

Science highlights or most popular articles

From the journals: JLR
Journal News

From the journals: JLR

January 28, 2020

Topics include fatty livers and hormones, how pathogens exploit lipid rafts and the lipoprotein–blood clot link.

Why you need more vitamin D in the winter
Wellness

Why you need more vitamin D
in the winter

January 26, 2020

With less exposure to sunlight in winter, adults should take in at least 600 international units per day of vitamin D from supplements or foods like oily fish, mushrooms and fortified dairy.

From the journals: MCP
Journal News

From the journals: MCP

January 25, 2020

Read about capturing a peptide link between migraines and opioid-induced sensitivity, profiling autologous body fluid exosomes and finding the RSK in melanoma protein interactions.

From the journals: JBC
Journal News

From the journals: JBC

January 24, 2020

Recent topics include misfolded tau proteins in Alzheimer’s disease, how enzymes trim peptides and how a parasite hijacks the immunity of its host.

Early immune response may improve cancer immunotherapies
Journal News

Early immune response may improve cancer immunotherapies

January 23, 2020

University of Illinois at Chicago researchers and colleagues report a new mechanism for detecting foreign material during early immune responses.

Do sperm offer the uterus a secret handshake?
Journal News

Do sperm offer the uterus
a secret handshake?

January 22, 2020

Why does it take 200 million sperm to fertilize a single egg? A female immune response is one reason. A molecular handshake may help sperm survive the bombardment.