By Kevin Beck Updated Aug 30, 2022
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Six elements on the periodic table—carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur—make up 97 % of the human body. Their abundance in the Milky Way is no coincidence; we are literally stardust, and these elements are the building blocks of life. The acronym CHNOPS helps remember them, though they are not evenly distributed—some concentrate in particular tissues and organs.
Carbon is the backbone of organic chemistry. Its ability to form single, double, and triple covalent bonds allows it to connect with virtually every other element. This versatility makes carbon the primary structural component of amino acids, the building blocks of proteins. Consequently, carbon-rich proteins form the framework of muscles, enzymes, neurons, and virtually all tissues.
Hydrogen, the lightest element, forms only a single covalent bond yet participates in a staggering array of organic molecules. It is integral to carbohydrates, lipids, and proteins, and together with oxygen constitutes the majority of water—the substance that makes up more than two‑thirds of human mass.
Nitrogen, though largely invisible as a diatomic gas in the atmosphere, is essential for life. It is a key constituent of amino acids and nucleic acids. The amine group (–NH2) that defines every amino acid contains nitrogen. In proteins, nitrogen-driven catalysis drives the biochemical reactions that construct and maintain tissues.
Oxygen is indispensable for cellular respiration and is also embedded in water, proteins, and lipids. Over Earth's history, atmospheric oxygen has risen from trace amounts to about 21 % of the air, underscoring its pivotal role in sustaining life.
Phosphorus is vital for cellular membranes and energy transfer. It forms the phospholipid bilayer that defines cell structure and is the backbone of ATP, the universal energy currency. Phosphorus also contributes to bone mineralization.
Sulfur is a minor yet essential element, found in the amino acids cysteine and methionine. It supports the structural stability of proteins through disulfide bonds and is critical in microbial metabolism, including sulfur-based photosynthesis.
Together, these six elements underpin every biological function—from the DNA that carries our genetic code to the ATP that powers our cells. Understanding CHNOPS offers a window into the chemistry that makes life possible.
