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

A proposal to use CRISPR to prevent opioid overdoses is a useless approach to healthcare
News

A proposal to use CRISPR to prevent opioid overdoses is a useless approach to healthcare

September 27, 2020

Nicholas McCarty of New York University writes that genetically engineering drug users’ brains is short-sighted, reactive and unnecessary.

Lessons from how the polio vaccine
News

Lessons from how the polio vaccine

September 26, 2020

Despite the polio vaccine’s long-term success, manufacturers, government leaders and the nonprofit that funded the vaccine’s development made several missteps.

From the journals: MCP
Journal News

From the journals: MCP

September 25, 2020

How marine iguanas mark their turf. A new way to study Parkinson’s disease. Glycosylation in influenza A. Read about recent papers on these topics in the journal Molecular & Cellular Proteomics.

Gut microbiome shaped by dietary sphingolipids
Journal News

Gut microbiome shaped by dietary sphingolipids

September 22, 2020

A new tracing method described in the Journal of Lipid Research offers clues on how a macronutrient interacts with the microbes that live inside us.

From the journals: JBC
Journal News

From the journals: JBC

September 21, 2020

Proteases that fire up the flu. A sulfate pocket to take out MRSA. Proteins that prompt cancer protrusions. Read about recent papers on these topics and more.

AeroNabs promise powerful, inhalable protection against COVID-19
News

AeroNabs promise powerful, inhalable protection against COVID-19

September 20, 2020

As the world awaits vaccines to bring the COVID-19 pandemic under control, UC San Francisco scientists have devised a novel approach to halting the spread of SARS-CoV-2, the virus that causes the disease.