User:MikeSadler11/CHON

= CHNOPS =

Summary
CHNOPS is an acronym that represents life's essential elements, Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, and Sulfur. Together, different combinations of these elements form biological macromolecules such as proteins, nucleic acids, and lipids, which are the building blocks of all living things on earth. CHNOPS are an important component of astrobiology research, which is the study of how life emerged on earth, and how life might exist elsewhere in the solar system and universe. Because life on Earth relies on the reactivity and characteristics of CHNOPS elements, and because these elements and reaction adhere to universal laws of physics and chemistry, it seems likely that life elsewhere in the solar system or universe would also be based on on CHNOPS elements.

This page focuses on the importance of CHNOPS compounds to life, their formation in the solar system, and origin on earth. For detailed information on the specific elements themselves, please see the respective linked pages.

Importance of CHNOPS in life

 * Carbon forms the backbone of biological molecules and is essential to the diversity of the organic compounds essential to life. Carbon has four valence electrons, which allows it to exist in many stable oxidation states, and readily form covalent bonds with a variety of elements.
 * Hydrogen is critical in chemical and biochemical reactions. Hydrogen is important to oxidation reduction reactions that life uses to gather and store energy for cellular functions, and build or degrade macromolecules. Additionally, hydrogen is a component of water (H20), a solvent for which biological reactions take place in and is essential for life to exist.
 * Nitrogen is an essential element of DNA, RNA, and in proteins. Nitrogen can exist in a wide range of oxidation states, from -3 to +5, and is involved in a variety of metabolisms and energy acquisition methods. Because many different forms of life use nitrogen in different ways, complicated nitrogen cycles are formed where the nitrogen is recycled.
 * Oxygen with hydrogen forms water, an essential component of life. Oxygen is highly reactive and play a critical role in biochemical reactions and the formation of macromolecules. Although many forms of life on earth use oxygen as a terminal electron acceptor during respiration, only the oxygen element, and not the O2 molecule, is essential for life.
 * Phosphorus is primarily found in life in the form of phosphate. Phosphate forms the backbone of DNA and RNA, and is a component of modern cellular membranes. Phosphorylation reactions, which transfer phosphate groups between molecules, is an important in the formation of macromolecules. Phosphate-phosphate bonds have high energy, and are used by all life to store chemical energy. This most frequently occurs in the formation of adenosine triphosphate (ATP) by the phosphorylation of adenosine diphosphate (ADP). The resulting ATP can then be used by the cell to drive non-spontaneous chemical reactions.
 * Sulfur is a critical component of proteins. Sulfur is in the catalytic residue of some enzymes, and provides complicated three dimensional structure to proteins through disulfide bonding . Sulfur is also a component of many coenzymes, which are required for catalytic reactions by some enzymes . Sulfur can also exist in a range of oxidation states from -2 to +6, making it important to metabolisms and energy acquisitions similar to nitrogen. Sulfur also has a complicated sulfur cycle where it is recycled by life in its many different forms.

Origin of CHNOPS
CHNOPS elements form the base of all life, and they must have been present in sufficient quantities on earth and played important roles in prebiotic chemistry (the abiotic chemical reactions that led to complicated, biologically relevant, macromolecules) that was a necessary for the emergence of life, also known as abiogenesis. However, these elements do not form the major components of the bulk earth (except for oxygen), which leaves the questions of how CHNOPS formed and how CHNOPS were concentrated for biospheres on earth.

Formation of CHNOPS
All CHNOPS elements (except for H, which is formed during the Big-Bang) are formed through nucleosynthesis, a reaction that occurs within stars that produces new elements. Some CHNOPS elements are formed during different stages during stellar evolution or by different kinds of stars. These elements are then ejected into the interstellar medium through solar winds or from supernova explosions where they may become incorporated into molecular clouds and ultimately form a protoplanetary disc.

Distribution of CHNOPS in the early solar system
As the protoplanetary disc (which was formed by the collapse of the molecular cloud) cooled, small particles could begin to aggregate, forming dust and eventually planetesimals around the young sun. The bulk material of the molecular cloud thus became the bulk material of the solar system. However, not all elements in the molecular cloud would become evenly distributed throughout the solar system. Some elements, such as silica, iron, and magnesium, are considered refractory, such that they can form condense under high temperature (approximately 1350K) and accrete closer to the young sun. Other elements, such as Hydrogen, are considered volatile and cannot form solids and aggregate unless the temperatures are much colder (approximately 100-300K). Thus, refractory elements are found in higher relative abundance in the inner solar system, and volatile elements are found in higher relative abundance in the outer solar system.

Origin of CHNOPS on Earth
The elements of the protoplanetary disc would accrete into dust and planetesimals, and ultimately become the planets we see in the solar system today. However, because not all elements are equally distributed throughout the protoplanetary disc, CHNOPS elements would become acquired on earth during accretion, and also later by delivery from comets and asteroids. For example, refractory Carbon is found in meteorites along the asteroid belt, but in concentrations approximately 1/10th that of carbon in comets, suggesting a depletion of carbon in the inner solar system or enrichment in volatile forms. Earth's mantle and crust is also thought to be a significant reservoir of carbon stored in carbonate rocks. Approximately 20% of Oxygen is found in refractory minerals while approximately 80% is found in volatile compounds such as H2O. This refractory oxygen would be present on early earth from accretion of dust and planetesimals. However, the volatile oxygen would be deposited and retained on earth much later, after it had cooled significantly. Sulfur appears to have both volatile and refractory origins, as FeS and H2S are found in abundance throughout the solar system. Phosphorus is depleted in several comets, consistent with the idea that it was mostly found in cometary dust, but it is also found in the refractory minerals apatite and schreibersite. Hydrogen is the most volatile element of CHNOPS elements. With the observation that outer solar system bodies are water rich, and inner solar system bodies are hydrogen poor, it is generally thought that earth's hydrogen source came primarily from the outer solar system.

CHNOPS on other planets
Through a combination of remote sensing, rovers, and orbiters, CHNOPS elements have been detected on inner solar system bodies including Venus and Mars with chromatography and spectroscopy. Some CHNOPS elements have also been detected on the moons Europa, Enceladus, and Titan. Spectroscopy methods have also identified CHNOPS elements in other stars, suggesting that some exoplanets should be equally enriched in CHNOPS as Earth. The identification of life's essential elements on planets and moons holds important implications for the potential for life to exist elsewhere in our solar system and beyond, and provides targets and objectives for future research missions.

Other elements important to life
While CHNOPS elements are the essential building blocks for life on earth, forming the biological macromolecules used by all life, there are many other elements that play essential in biological processes. Many metals play critical roles in biological processes by enabling enzymatic function. Iron (Fe) is an important electron carrier in metabolisms and is essential to most life. Molybdenum (Mo) is a critical coenzyme for Nitrogen fixation, and Magnesium (Mg) is an essential component of chlorophyll photosystems that are used to use energy from sunlight to convert CO2 into sugars during photosynthesis. Zinc (Zn) is essential to many enzymes with DNA binding properties. These metals are important because of their redox states or catalytic properties that enable chemical reactions and enzymes to function.